ITEM NAME:2x Electric Roto Starter Back Plate for 1/10 HSP 16/18/21/25 Engine Parts .like-pro-float .like-pro-price-both{clear: both;.Suits 12mm hex one-way bearing. 2 Pieces 11011 Drill Plate. Suitable for: Vertex 16/18/21/25cxp; SH 18/21 Japan-18cxp; 18/21/27 Nitro engine. Hole center to hole center: 27mm. Not suitable for engines larger than. 18 (.19 + etc), Not suitable for 1/16 engines (.07 or. 05 for example).