If it was on a Homelite XL870 it for sure has been filed out to 3/8's. The tail is too narrow to fit well on the large frame Homelites and I'm willing to bet that was a early Husqvarna 9mm slot bar or a early Poulan/Echo 5/16" slot. The tails of the XL style Homelite mount, the Husky , Pioneer and Poulan mounts are virtually the same size with just different size slots and adjuster hole designs.