someone else just had that problem with the cfm boot, i think i ordered the 2.25 x 2.5 boot, for my 34mm pj, but i'ts been so long, and im old and senile, hahaaa, but i'd measure both to be sure
i think heres the link..............
Pipe Reducer
i'd get the clamps from them too, <worked good, cheap, and came in like 3 days