1.) See Engine Block
2.) In some cases, t' thrust rin' is part o' t' motor. It may be part o' t' aft closure, or a flanged permanently mounted on a single-use motor. 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, shiver me timbers, 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). Avast! Without a thrust rin' (or engine block), t' friction fit technique would need t' be used.