One of the challenges we faced in designing the RMU-Mk3 was the variation in pass through fittings. The fittings can be 1/8 BSP or 1/8 BSPT and there is a marked difference between them. Printing threads for such fine detailed fittings was not an option so we had to come up with something that would allow fitting of different sizes. 

If the holes were too loose, the threads would strip out and if they were too tight they would crack the PETG material. Alan came up with a clever design to work around this problem without the need for inserts.