If finding the nipple size is the only snag, that should not be too difficult. It's most likely going to be either 1/4X28 or 5/16X24, could be an odd thread but I doubt it. Just go to the hardware store and get a few bolts in 1/4 and 5/16 size. Try to get both coarse and fine threads and I'll bet one will fit. You might also call Track of the Wolf, they're nice and knowledgeable folks and glad to help.