"Trying to fit some Continental taps that come supplied with flexible hoses that look just like standard 15mm parts but they are too small when you try to fit them. Screwfix, their very helpful staff and this little part to the rescue. Quite literally the only way to make the taps fit!"
"needed a coupler for grohe monoblock tap tails 3/8 bsp thread and being a retired engineer took a guess that 15mm to 12mm coupler would have a 3/8 thread on the 12mm side and was right ! will keep a couple of these fittings in my toolbox in case i come across this size of tails again !"