F connector coupler with nut and washer (also see our F connector Back to back couplers [without nuts & washers])
These are often used mounted in patch plates. The amount of “spare” thread on the barrel (after having screwed on the F Connector) is obviously critical. We have to buy in the F couplers with the nuts and washers, then transfer the latter onto our F BtoBs because the barrels on ours are 1mm longer ! And it’s a lot of farting about……. The gap (with our F connectors) is as per the graphic below. Note : we can only guarantee this gap with our F conns.
If you’re desperate and your Fs won’t quite screw up fully because you have not got enough thread protruding from the connector (once installed in the patch board) you could try grinding off some of the F connector, though this is a last resort, obviously….