The 10 round inserts that went into regular USGI mags are compatible only with the USGI M261 .22LR adapter. You didn't say what "flavor" of adapter you have, but if you have an M261, your only option for greater-than-10 round mags is Blackdog, and even those are damn hard to find.
They hold 10 rounds, and insert into any USGI mag, 20 or 30 round. They are, as I said, only for use with the M261 .22LR adapter, and are incompatible with the more popular Atchisson/Ceiner style adapter, like the Spike's, CMMG, etc.