That is an incredibly difficult question to answer. There are so many variations, especially when considering a FEL or backhoe that it requires a bit of guessing.
Perhaps a parts diagram may have the information but my advice is to take one out (if available) and take it to a reliable and well-equipped auto parts store. They can measure the threads and give you an identical Zerk.
Note: I have tried buying several assortment kits of both standard and metric threads but finally had to go to a parts store to get the correct size. Trial and error just did not work.