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How to Disassemble and Reassemble a Parker “51”

(This page published February 1, 2024)

Reference Info Index | Glossopedia  ]

Fountain pen Vacumatic-filling
Fountain pen Aero-Metric Mark I and Mark II
Fountain pen Cartridge/converter
Fountain pen Squeeze-filling Mark III

The Parker “51” is arguably the most collectible vintage pen in the world. It was produced in great numbers, in several mechanical variants, in many colors, and with a broad variety of cap styles. The numbers produced make the Vacumatic-filling and Aero-metric models relatively easy to collect, although some of the colors and cap styles are uncommon enough to present an exciting challenge. The cartridge/converter version is far less common, and examples of the notorious Red Band version are scarce indeed. This article does not discuss the Red Band version because it was not built to be disassembled for repair of any type. Given its rarity and the difficulty of disassembling it without damage, the Red Band version is best consigned to a display role instead of being used. This article also omits discussion of the 2002 51 SE and the 2020 reboot, both of which are built internally more like the Parker 45 than like the original “51”.

What all of the “51” variants share is their cylindrical hooded nib, but beyond that there are enough differences that a treatment of how to take a particular “51” apart and put it back together is not a single easy 1-2-3 list of steps. Except as indicated above, this article discusses all the known versions and how to deal with them. Rather than repeat material from other articles that is not directly related to disassembly and reassembly, the text includes links to those articles as appropriate.

Tools Required

Parts Required

Supplies Required

As you follow the instructions in this page, refer to this general diagram of an Aero-metric pen to identify the various parts. Differences between pen versions will be pointed out as needed.

Fountain pen

There is a complete discussion of the anatomy of the Aero-metric ”51” in the article Anatomy of a Fountain Pen IV: The Parker “51” (Aero-metric Version).


Before the serious process of disassembly can begin, remove the cap and set it aside. If you are working on an Aero-Metric or cartridge/converter pen, remove the barrel and set it aside. Soak and flush the pen thoroughly to loosen and remove any ink residue, especially in the threads.

Dried ink does not release under heat, and too much force can break an ink-locked pen.

Removing the Shell

The “51” shell (hood) screws onto the front of the pen’s body. In most examples, the shell is secured against loosening or leakage by shellac on the threads. At some point during the 1950s, however, Parker revised the attachment method for the Aero-Metric version, substituting an O-ring for the shellac. This change yielded a pen that was easier, quicker, and less likely to be messy to assemble than before, but unanticipated problems with loosening and leakage became apparent after the pens had been on the market for a while, and Parker reverted the design to the shellacked version. Many of the O-ring type pens today will be shellacked together but will have a space in the back end of the shell where there was an O-ring. Some workers leave the O-ring in place but use shellac, too, for extra security.

Removal of the shell for all versions is essentially the same: apply gentle heat to the shell in the area adjacent to the clutch ring, and use section pliers to unscrew the shell. The plier should grasp the shell as close to the clutch ring as possible. Depending on which version you’re working on, use the other hand to grasp one of these ways:

Grasping the shell midway along its length, where it has no internal support, can crush it, resulting in irreparable cracks.

If the shell won’t come with relatively little effort, it might need more heat and patience.

Removing and Disassembling the Collector Assembly

With the shell off, you can remove the collector assembly.

The cartridge/converter version does not have a collector. In the collector’s place is a solid filler block that holds the nib and feed in the same manner as a collector but does not extend into the connector. Only the end of the feed extends into the connector.

Before removing this assembly, however, you can save yourself some future effort by marking the barrel or connector in line with the center of the nib. In the cartridge/converter version, unfortunately, the filler block/nib/feed assembly is not secured against rotation. It might have rotated with the shell, and marking the location in which you find it might be less than useful. In any case, there is no good location where you can place a mark in the cartridge/converter version. For the other versions, do not use the broad air channel in the collector as a guide; during the 1950s, Parker issued a service bulletin saying that the channels in the collector need not be aligned with the nib and feed, and many pens were assembled in the factory without these parts aligned. Decades’ worth of experience has taught us that the alignment is important — some pens will simply not write properly if they are not aligned — and there are instructions for making the alignment correctly later in this article. Mark the location with an X-acto knife applied to the side of the connector or barrel projection that holds the feed, as shown here.

Marking the connector
The more accurately you mark the location for the top center of the nib, the more likely it is that you will get a good alignment easily when you reassemble things. Even so, however, if the nib and shell were not aligned before, or if you do not do a good job cleaning out old adhesive, alignment can be a trial-and-error process.

To remove the collector assembly, grasp the collector gently with your fingers. Applying gentle pressure to avoid breaking the collector’s fins, rotate it slightly back and forth to be sure it’s free, and slide the assembly out of the barrel or connector. There should be a little frictional resistance as you do this; that resistance is what keeps the collector from rotating when the pen is assembled. If the collector does not want to slide out, it’s likely that it’s ink locked, and a trip through the ultrasonic cleaner will almost always loosen it so that you can remove it with your fingers. If that does not work, as a last resort you can grasp the collector from the side with a section plier as shown here. Applying gentle pressure to avoid breaking the collector’s fins, rotate the collector assembly slightly back and forth to break the stiction, and then work the assembly out while you continue rotating.

Removing th collector assembly
If you need to resort to the section plier trick, you should be aware that you are taking your collector’s life in your hands. It might be time to send this pen to an experienced professional.

To take the collector assembly apart, start by removing the nib. Hold the collector by the back end, where there are no fins, and grasp the nib between the thumb and index finger of your stronger hand. Rotate the nib slightly back and forth to break the stiction, and then work the nib out while you continue rotating.

Removing the nib

The breather tube is attached to the feed. Remove the two parts together in the same manner as you removed the nib, being careful — especially with the Mark I Aero-metric version — not to apply any force to the breather tube. The breather tube in the Mark I is sterling silver, and it is very easy to break this tube off where it enters the feed. At some point, probably related to the Mark I/Mark II transition, Parker started using collectors of molded black plastic and breather tubes of rigid black pastic tubing,. These parts are less fragile than the parts they replaced.

In pens made before the early 1950s, the feed is deeply cut away at the front for about half its length so that it is only a half-round. (See the first and second photos under Disassembling What’s Left.) Be careful with these feeds because this half-round part of the feed is much less strong than if it were fully round, and it’s possible to break it by twisting too hard if it is ink locked.

The cartridge/converter version has no breather tube, but its feed is often a very tight fit in the filler block. The best way to get it out is to place the assembly on a nib knockout block with the front end downward and use a drive punch of the appropriate diameter with a jeweler’s hammer to drive the feed out carefully, with light taps.

The plastic material of which the cartridge/converter version’s feed is made is brittle, and the part projecting from the back of the filler block can break off if you are not careful to drive the feed straight out.

Removing the Clutch Ring

The clutch ring fits onto the front of the barrel or the connector. It is a simple slip fit, but it is sometimes stuck in place either by shellac or becaused it’s ink locked. Shellac will respond to gentle heat, and ink will respond to soaking in cool water. You can remove shellac residue with Simichrome; be sure to get all of the Simichrome off, or you’ll need to clean off that ugly pink powder film later.

Disassembling What’s Left

From here, there is not much left to do to finish disassembly. The following short paragraphs, each with a photo, will show you the parts of their respective versions, laid out here in the order of their assembly, front to back.


Reassembling a “51” is basically just reversing the disassembly, but the following sections describe things that require additional guidance. First and foremost, I recommend that you assemble the back end of the pen before assembling the front end. Refer to How to Replace a Pen Sac for instructions on assembling the back end of a Vacumatic pen.

Reassembling the Aero-metric Sac Guard to the Connector

If the sac guard is either of the two press-fitted types of sac guards, you can simply push the dac guard back into place on the back side of the connector. However, if the sac guard is so loose that it rotates freely on the connector or threatens to come off as the pen is handled, I recommend that you apply shellac sparingly to the appropriate area of the connector before assembling these parts. Shellac will hold the sac guard securely, yet it will soften with a little heat should you ever need to remove the sac guard again. Only a little shellac is required, and you should remove any that is squeezed out of the joint onto the exterior surfaces using Simichrome.

If the sac guard is threaded, don’t worry about using any adhesive. Look for a whitish powdery residue on the threads mof the connector and inside the open end of the sac guard. (This whitish powdery residue, if there is any, might remind you of dried Simichrome in appearance, but it’s really corroded aluminum.) Clean away any residue from both parts, using a nail brush for the connector and a " (6.4 mm) tube brush for the sac guard. Screw the sac guard in place without adhesive, firmly enough that it will stay but not so tight as to damage the plastic threads of the connector.

Replacing a Breather Tube

It is rare that you will need to remove a breather tube from its feed. Such a need is most likely to arise if the breather tube is sterling silver and has been corroded by the use of "51" or Superchrome ink. Silver breather tubes do not like to come out of the back of the feed. The best way to repair a pen with a corroded breather tube is to find a replacement feed/breather tube assembly. Removing a sterling breather tube without enlarging the hole in the feed requires an insanely steady hand or a machine lathe; if you are able to do this, you can buy newly made exact-replacement breather tubes of stainless steel from

Plastic breather tubes in Vacumatic-filling and later Aero-metric pens will pull right out of the feed and can be replaced easily with semi-rigid plastic tubing. (Although Parker used rigid tubing, the breather tube in an Aero-metric pen does need to be rigid.) The tubing should have an outer diameter of 0.070" (1.8 mm) and a wall thickness of about 0.015" (0.4 mm).

There are two different cut lengths for Vacumatic-filling pens:

The lengths given above are a little less than half the length of the space available. This obviously reduces the pen’s ink capacity by half, but Parker figured out in the mid-1940s that a truly full reservoir would leak when carried in an airplane, even if the pen was carried nib uppermost. From 1946 on, the breather tube was cut shorter (U.S. Patent No 2,400,768) so that the level of the ink when the pen was carried nib uppermost would fall below the end of the breather tube; thus, no ink could be forced up the breather tube to cause a leak.

There are also two different cut lengths for Aero-metric pens:

For either Aero-metric version, use a No 77 drill (0.018", 0.546 mm) to drill a hole carefully through one side of the tube approximately " (9.5 mm) from the end that you will insert into the feed. Drill slowly and carefully so that you actually remove material instead of just poking a hole, and be sure to remove any shavings left stuck to the tubing from the drilling operation. If this hole is omitted, the pen will leak when carried in an airplane, even if it is kept nib uppermost.

Reassembling the Nib/Feed/Collector Assembly

Here is where we have the opportunity to correct a mistake that Parker made in the 1950s, when the engineering department issued a service bulletin saying that the channels in the collector need not be aligned with the nib and feed. That service bulletin was wrong. Alignment does matter.

It’s easy to align the nib the way Parker did at first because the notch in the back end of the nib is the same width as the air passage in the collector. But this top-side alignment is not the one to worry about. (Collectors were machined to very tight tolerances, but the exact alignment of the slits and slots in the collector relative to each other was not considered to be really critical. (The later plastic collectors have their slits and slots aligned correctly, as the alignment there is a function of the accuracy of the mold.) What’s important is that the slot in the bottom of the nib be aligned with the full-length slit in the collector, opposite the broad air passage, as shown in the photo below.

“51” nib alignment

Install the feed and breather tube first, aligning the underside of the feed as closely as possible with the full-length slit in the collector. be sure the feed is seated all the way; some feeds will tend to stick a short distance before they are fully seated, requiring a firm push to get them to go the reste of the way. Be careful as you do this that that you push the feed straight in, being careful not to break off the front end of an early feed by pushing with some sidewise force. Then install the nib, aligning the slot in its underside with the same slit in the collector.

Reassembling the Front End

If you removed the clutch ring from the barrel or connect, reinstall it now. Do not use adhesive; if you do, that will just mean that the next person who has to disassemble this pen will curse you to the high heavens.

If the pen originally had an O-ring, you can reinstall that O-ring, replace it with a new M1.0×7 O-ring, or leave it out entirely. Shellac will be the actual sealant.

If you marked the alignment of the nib before disassembling the front end, insert the collector into the fromt of the barrel or connector, as appropriate, aligning the nib with your mark to the best of your ability. Gently push the assembly home.

If you did not mark the alignment, screw the shell onto the front end of the barrel or connector, screwing it all the way down firmly but without shellac. Stick a small piece of masking tape or blue painter’s tape to the clutch ring, not allowing the tape to extend onto the surface of the shell, and use a Sharpie-type marker to mark the orientation of the shell’s pointed end. (Relocate the tape if necessary.) Then remove the shell. Rotate the collector or the filler block as necessary to align the nib to the bedt of your ability with your mark.

Apply shellac to the threads of the barrel (Vacumatic) or connector (non-Vacumatic) and reinstall the shell, aligning its point with the center pf the nib. If the shell turns further without noticeable resistance, remove the shell and realign the nib slightly by turning the collector or filler block a little bit clockwise. Reinstall the shell and see whether the alignment is good. If it’s not, you will have to repeat this process until you’ve gotten the alignment perfect. (In this instance, “close” is not close enough.) If the alignment ends up close but not perfect, take the shell off, rotate the collector assembly a tiny bit in the appropriate direction, and reinstall the shell. You get about two tries before you'll need to refresh the shellac (which might mean removing some of what’s there first). When you get it perfect, use Simichrome to remove the shellac that has been squeezed out of the joint onto the exterior surfaces. If none squeezes out, you probably did not apply enough.

  1. The Mark III is not a true Aero-metric pen. Instead of the long breather tube with a tiny transverse hole near the back of the feed (U.S. Patent No 2,612,867) , it has a short breather tube without that hole, like the 1946 and later Vacumatic versions.  Return

The information in this article is as accurate as possible, but you should not take it as absolutely authoritative or complete. If you have additions or corrections to this page, please consider sharing them with us to improve the accuracy of our information. My thanks to Mike Kennedy for his having encouraged me to write this article.

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