Was a perfect fit for my 1994 Tracker ProMariner 60HP 3 cylinder motor for the vent plug.  The previous owner had installed this screw so much that I could not get it to break loose.  I actually ended up stripping it more than it was and had to go buy a manual impact as my 1/2" Dewalt Impact could not loosen the screw (http://www.amazon.com/Lisle-29200-Hand-Impact-Tool/dp/B0002NYDRG  <looks similar to that but purchased for $6 dollars at a local True Value Store).  I paired this with the lower drain plug (http://www.amazon.com/gp/product/B000O7H8FE?redirect=true&ref_=cm_cr_ryp_prd_ttl_sol_4) for changing out my lower unit fluid.  I can see these not lasting more than a few changes due to the maleable steel used for them but definitely recommend these!