Pneumatic Air Reservoir End Nut Size

Hi all. Can someone tell me what the big nut size that’s located at each end of the air cylinder?

I’ve searched this form and google, but to no avail… Vex doesn’t appear to sell this part individually either, and their pneumatic system is not in stock. I just need the nut for the expansion mechanism.

thanks much!

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I believe it is 3/4-16UNF.


First, before you spend too much time shooting giant nuts across the field, have you considered alternatives?

To answer your question, which takes a bit more than a google search, here is the technical information you need and where to find the answer:

The air tank is made from NCM-series air cylinder components, it is basically an air cylinder with the piston and piston rod left out, and a cap on both ends. Here are the specifications for all the NCM-series air cylinders: Assuming you don’t want to search the technical specs too hard, you’ll find on page 18 of the pdf (“page 10” of the document) that the nut for a 1-1/2" bore cylinder is a 3/4-10 nut. BUT: it’s not a regular nut, it is probably a “thin” nut (also called a locknut). To meet the requirements of the Game Manual, rule R7-i, you need to match the material as well as size, so you’ll need a stainless nut. Here’s a source that should be ok, but purchase at your own risk: McMaster-Carr

BUT, before you buy a bunch of nuts, consider this: If you don’t already have a second air tank (or you’re part of a larger organization with multiple teams), would it make sense to just purchase a spare air tank (and you’ll get a pair of VEX-legal nuts)? Alternatively, there may be an organization who is not shooting their air tank nuts across the field because they have found a better way, and perhaps they could contact you about giving/selling/trading one of theirs. (I might have a spare, but our workspace is still closed for the holiday until classes start again).

You can purchase air tanks from SMC or a third party industrial supplier like Radwell: US14227-S0400 by SMC - Buy or Repair at Radwell - . You’ll also need air tank fittings: KQ2H03-34S by SMC - Buy or Repair at Radwell -


That isn’t the only thing that works for expansion. Another possible solution could be a ziptie with 6-8 nylocks on it. when you close the ziptie, then it will have a similar weight and shape to a large pneumatic hexnut.

Experiment with different weights and record it in your notebook. We don’t have Pneumatic Nuts either, so we have to use ideas like this in order to get similar functionality.


I was typing without thinking. The UNC size is what we use all the time in my company, so “autopilot” kicks in. And the new forum doesn’t let you edit your posts, which is really annoying since you see all your typos right after you hit “reply”…

But I still stand my my first statement, there’s many better alternatives than shooting giant nuts across the field!