To find correct thread on standard or metric for nipples or screws I buy the nearest sizes above and below in as many different thread types as possible in screws or bolts. Then after cleaning the hole as well as possible try different screws/bolts till I find the one that fits. The screws and bolts are cheap easy way to find out what fits. I have made nipples from small bolts until I could find one. Hardware, auto parts, etc have a good assortment of metric and standard screws and bolts.