A rin' which is glued into t' motor tube t' contain t' motor durin' thrust, 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. Without a engine block (or thrust ring), me bucko, t' friction fit technique would need t' be used.