A rin' which is glued into t' motor tube t' contain t' motor durin' thrust, ya bilge rat, preventin' it from movin' forward into t' motor tube while allowin' ejection charge t' pass into t' body o' t' rocket; typically a cardboard rin' or section o' a used motor casing; normally only used in LPR. Often unsed interchangeably with Thrust Ring. Avast, me proud beauty! Without a engine block (or thrust ring), ya bilge rat, t' friction fit technique would need t' be used.