I have a bath tap with a parallel male thread.
I've bought an adapter to mate with the tap & accept 22mm copper via an olive compression fitting. I feel though that the adapter should have included a washer as I'm uncertian that the adapter will seal on the parallel thread. Will a washer be reqd and is it normal to have to buy these separately?
By the sound of it you have bought what is known as a 22mm x 3/4" Female Iron.
It's possible to use this fitting, however it is more difficult to seal to the thread on the tap, it does not come with a washer and PTFE tape is normally used to seal the threads.
The usual method is to buy a 22mm Tap Connector. These are more commonly made as solder fittings but compression types are available. This fitting comes with a captive swivel nut and washer (3/4") on one end and the 22mm copper fitting on the other......
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