The word "taper" implies a gradual reduction to my mind, but this doesn't square with the whole purpose of a thread.
Reason behind this is my researching an alternative set of tails for a bar mixer for a power shower. I've bought a 3 bar pump and the book tells me to run the output in 22mm as far as practical. We picked up all the fittings for our new en-suite in the sales in January, and it's only now that I've got round to taking a closer look at the plumbing. My plan is to run a pair of 22mm copper pipes down a stud wall cavity and then turn these out ninety degrees into the shower bay and connect to the mixer bar. The mixer bar comes with a pair of dog-leg fittings - three quarters bsp male on one end, half inch bsp male on the other. When you look inside the dog-leg the aperture is (roughly) ten millimetres. From a 22mm pipe down to 10mm feels wasteful, hence this quest to find a better fitting.
On my desk is a 22mm female to three-quarters male straight BSP fitting courtesy of Screwfix. The BSP thread isn't deep enough to attach the mixer bar (the mixer bar nut grounds out before it tightens: no use). Ecstasy would be an elbow joint taking 22mm copper pipe on one end and having (say) a two inch long 3/4" BSP male thread (so I could cut it down if necessary) on the other end. I could even find a nut for the 3/4" thread and attach the fitting to some marine plywood as part of the install (someone here posted a URL of some pictures on how they did this: can't seem to find it - would the owner reply please with the url?) I suppose a 22mm female elbow connecting to a 3/4" bsp female could be of use, especially with some "barrel nipples" (found via another thread here on uk.d-i-y; all the jokes on this phrase also covered too).
Any help appreciated; thanks in advance