Ignorant question, probably. I've reloaded for 25+ years but always rifle cases with large rifle primers. Now I want to load 223Rem and 38 Spl. I have an old RCBS Rockchucker press, which I bought as a kit, with the manual spring-loaded primer arm and aluminum tube. The kit had both size primer tubes, but if it had the small primer sleeve and plug?, I have lost them. I thought I had found the parts on eBay, but what I got is not threaded, though it is similar in length to the large primer plug I have. Can anyone tell me what part number I need to order?

You need to call RCBS, or just visit their web site. The older primer plugs aren't threaded; they are held in place by a set screw. How long you been loading?
PN is RCBS 9553. Midway is out.

I just found a parts list online. You are right about the part number (09553).

I just guessed as to how long I've been reloading. I'm older than shit and been loading a long time.

Anybody need one of the older unthreaded ones???

RCBS says I can buy one from them for $4.99. I think I will.

mine are unthreaded, set screw also

If you call RCBS, my money says they will send you a new small primer seater gratis. I have called them regarding items I had lost, and they replaced them for nothing. 1-800-533-5000 will get them, I believe.

Best service in the handloading industry, IMHO.

Now that I have an unthreaded one that I don't need, anybody have a guess as to its part number? I have acquired the newer threaded version. Thanks for the help!