My friend gave me a John Deer trimmer (model BC1600-UT15198), but it needs a new spool. I bought one of those Echo spools, and it comes with adapters to work with the John Deere trimmer. It came with two sizes of bolts to use for threading into the shaft, but none of them fit. The 1/4" bolt is too small, and the 5/16" bolt is just a little too big. I even tried a metric bolt that is in between those sizes, but it doesn't fit. Any suggestions? Thanks for the help.