How to Replace O-Rings on a Bostitch Nailer or Stapler [VIDEO]

Contractors have to replace the o-rings in their staplers and nail guns periodically because damaged o-rings can lead to air leaks. If you find that your nailer or stapler isn’t performing at its peak, its o-rings might be in need of replacement.

Here’s how to replace the o-rings in a Bostitch MIIIFS. (If you know that o-rings are not the cause of your troubles, here’s our guide to troubleshooting common nailer problems.)

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Step 1: Make sure you have all of the necessary tools and equipment.

The Bostitch MIIIFS and MIIIFN each come with a special kit for replacing the tool’s o-rings, as well as a repair kit. These kits contain all of the tools you need to perform this repair. Need a new o-ring kit for your Botitch MIII? Click here to buy one online. 

With most other nailers and staplers, you can use standard tools for the o-ring replacement process.

Step 2: Disassemble the entire nailer/stapler from the top down.

To remove the top cap, take out the four allen head screws. Take out the three screws on the poppet actuator to remove the actuator. Then remove the shoe base to access the bumper.

Step 3: Remove the poppet from the piston stem mechanism.

If you’re working on a Bostitch MIIIFS or MIIIFN, use the special wrenches included in the tool’s kit to perform this step.

Step 4: Remove the external and internal o-rings located on each part, and thoroughly clean all of the parts.

You want to clean all of the parts using tool oil in order to remove any grease, dirt, and debris that has built up over time. You should also take this opportunity to inspect each individual part for damage, because leaving a damaged part in your tool can really harm your equipment.

Step 5: Add new o-rings to the nailer/stapler.

Before installing the new o-rings, apply a slight film of o-ring grease to each one. You should also apply some more tool oil to the moving parts to facilitate reassembly. Be sure to use the appropriate grease rated for the o-rings used in your application.

Step 6: Reassemble the piston mechanism, poppet head, and driver assembly using the wrenches in the tool’s repair kit.

Step 7: Tighten the assembly so the plunger is flush with the top of the poppet.

Step 8: Test out the tool to make sure that it’s functioning properly and  the problem has been fixed.

If you find that your tool still isn’t functioning correctly, the source of your problems is probably something other than o-rings. Check out our blog post about common nailer problems.

You can prevent your newly installed o-rings from wearing down quickly and becoming damaged by adding enough tool oil to your nailer or stapler—typically, it needs two to three drops of oil a day to maintain its peak performance.

For more information on Bostitch products or replacing the o-rings in your tools, call us at (800) 787-1786 or email to speak with a hardwood flooring professional from our in-house equipment repair shop.

5 thoughts on “How to Replace O-Rings on a Bostitch Nailer or Stapler [VIDEO]

  1. Brad

    I had a problem with my Miii FN with air leaking out from the exhaust. I cleaned it and replaced all the O-rings (ORK6 kit). Reassemble and the same problem exists. There is one part of the ORK6 directions that I don’t understand. Tighten the assembly so the plunger is flush with the top of the poppet. I just tightened the plunger down as far as it would go on the stem. I don’t have the special tools that you use in the video. I’m assuming that the wrench under the poppet holds it up a bit. Perhaps tightening the plunger all the way on the stem is what’s causing my problem. Can you tell me how far the poppet should be held up from the top of the piston when tightening the plunger? This is the only thing I can think of that may be causing the leak after replacing all the O-rings.

    1. City Floor Supply Post author

      Hi Brad,

      Thanks for reaching out with your question.

      The “stem plunger” should be tightened flush with the “piston stem”. Use Loctite 242 to prevent it from coming loose. Also, when all o-rings are replaced you should have 5 extra o-rings left over. These are not necessary for this style gun. Don’t forget the small clear o-ring inside the poppet located near the 4 holes. This o-ring is the main one that leaks. Be generous with the supplied lube that comes with the kit.

      Hope this helps. If you have any additional questions, feel free to call us at (800) 737-1786.

  2. Brad

    Thanks for the response. After doing the ork6 ring replacement again (new set of rings) in case I knicked one or something like that I realized that the kit does not include the head cap oring. I’ll order one of these as it seams that could be the issue. Installing the second set or orings did not resolve the issue. Thanks Brad


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