I'm a total newbie with HO trains. I've been buying engines and cars, mostly on ebay, for my grandson. Most are Bachmann. Some are missing couplers. One arrived with a loose coupler and I couldn't find the screw for it. The coupler on the other end of the car is mounted with a small round-head screw. The coupler has a small hole for the screw. On ebay I bought some Bachmann EZ-Mate Center Shank Medium no 78005 couplers, but the mounting hole is too large to hold the screw head. Can anybody tell me where to look? This is my first day on this site. I know I must sound pathetic, but thanks for some education.