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Custom Scuba Tools MK 5 and MK 10 Piston Stem O-ring Tool

Mon Aug 12, 2013 9:40 pm

MK 5 and MK 10 Piston Stem O-ring Tool

I just received my new toys from Herman and I am impressed to say the least. Herman’s Custom Scuba Tools MK 10 and MK 5 piston stem o-ring tools makes installing the piston stem o-ring an easy task. If you've ever attempted to install the piston stem o-ring, you know it can be a chore unless you have a specially designed tool to do so.

At first glance the Custom Scuba Tools device looks very similar to the other tool available.

They also operate based on the same concept; however there are some important differences. The older design when used without mounting it to a tank or held by some other method is very awkward.

Thanks to the design of the Custom Scuba Tools lower guide, it can be used on a flat surface such as a work bench or table.

The o-ring insertion rod of the currently available device is a single diameter and will pass through the regulator body and o-ring. A close inspection of the CST insertion rod reveals a couple of improvement Herman incorporated into his ingenious design. The insertion rod is machined in a fashion so that only the end of the dowel will fit into the o-ring groove. This prevents the rod from pushing the o-ring past the groove into the high pressure chamber. The same end of the rod has a slot which guides the o-ring into place. A 360 degree twist of the rod seats the seal in the groove.


My very first attempt at installing a new o-ring was successful and took 10 seconds flat. Compare that with having to first mount the regulator body in a vice or on a tank valve and it is easy to see why this design is superior.

The Custom Scuba Tools o-ring insertion tool is competitively priced and much easier to use than the tool currently available. Note that the MK 5 and MK 10 tools are separate tools, so if you need both mention it to Herman.

Look for Custom Scuba Tools on eBay, at ... d=15502679 or PM Herman.

Another well made tool from Herman-thanks.

A sincere THANK YOU to all at VDH who make this wonderful resource available and to all the thoughtful contributors.

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