1.) See Engine Block
2.) In some cases, t' thrust rin' is part o' t' motor. Avast, me proud beauty! It may be part o' t' aft closure, or a flanged permanently mounted on a single-use motor. Avast! T' purpose is t' prevent t' motor from pushin' up into t' motor mount while t' rocket is under thrust. In absence o' an engine block or built in thrust ring, many rocketeers will make a thrust rin' by wrappin' maskin' tape around t' last 1/4" t' 1" section o' t' motor (dependin' on motor size). Aye aye! Without a thrust rin' (or engine block), t' friction fit technique would need t' be used.