Weirdly, Tone, I'd never looked until you asked.
The original Weihrauch steel Spring guide was made from 14mm OD, 10mm ID seamless tube, these were made the same seamless tube that Weihrauch still use to make the underlevers on the HW77 and HW97 :-
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Then Weihrauch changed to using a two piece assembly with a nylon guide fitted into a steel base washer, from what I have to hand the 25mm HW30 has a different sized nylon (13mm) and washer to the 26/30mm guns.
The HW30 parts are not interchangeable with the 26/30mm parts.
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As far as the 26mm and 30mm cylinders go the base washers and nylons are all interchangeable but from what I have here they're all about the same size nylons at 14mm.
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I only tend to use these genuine Weihrauch guides on springs with an ID slightly less than 14mm by machining them down to fit the chosen Spring.
To fit a Weihrach guide to the HW50 I've just built up I machined a 26mm base washer down to 25mm and then selected the best fitting nylon inside the 20mm OD Spring.
If I build a gun with a Spring with a larger ID than 14mm I normally end up machining a stainless steel Spring guide.