These 1/4" compression fittings are made from 304 stainless steel. They connect to 1/4" main supply hose to anything that's threaded with 1/8 BSPP (also referred to as "G-thread"). Classic systems from the UK can be well-developed but also challenging to work with due to rare thread types. Here's a means to enjoy sophistication and convenience at the same time. Adapt common tubing, solenoids, and other plumbing elements.
Conventional in appearance, these are actually two pieces that thread together with the hose secured in between.
Assembly is as easy as it looks. Pass the tubing through the nut and then force it over the barb. Next, tighten the nut on top of the bulged line with hard finger torque. Secure with weak thread locking fluid, if you please.