3/4" Bibcock output thread size ?

You need to measure threads and compare with sizes here:

A 3/4" BSP fitting has a thread > 1"

For an example of a reducer 1/2"M x 3/4"F:

I would hope you can get one locally, or with a better price on postage!

When they arrive I have absolutely no problem measuring them but they haven't arrived !!!!!

Ah yes, that might help.

Can you supply a manufacturer's part number?

I'm pretty sure the tap will be 3/4" BSP.

If you want to match this to Hoselock items:

I've met 7/8" - but I've led a sheltered life as an office wallah so that counts for little. I certainly don't suggest it is a (let alone _the_) standard.

I think reducers to 3/4" can be bought - or contrived by cunning artificers :)

Still not got them but I'm pretty sure that they are indeed 1" BSP on the outflow side - sufficiently convince to buy the Hozelock male fitting for 1" BSP which is significantly more expensive that the 1/2 and 3/4 sizes:

Andrew

very probably given my history for being wrong :)

That's about half what my brother tells me the 7/8" equivalent cost his allotment club - albeit they bought locally. (That also reminded made belatedly that 1" BSP is 11 tpi while 3/4 and 7/8" are 14 which might have helped if you'd a photo of the tap.)