This is the 55mm Folding Propeller Hub for a 50mm Spinner from Advanced Precision Composites. For use on Electric powered aircraft only (not for gas engines). FEATURES: Two-piece, Gray composite propeller hub that goes on each side of the folding propeller blades to hold them in place (blades are not included, see REQUIRES) Hub has molded nut insets for easy tightening Comes in a bag attached to a header card INCLUDES: One composite propeller hub Two 3x10mm cap head screws Two 3mm nuts Two 3mm washers REQUIRES: Propeller blade sets (use APCQ4305 through APCQ4360) 2.5mm hex wrench (GPMR8012) to tighten cap head screws Hand and eye protection when operating propeller SPECS: Overall Length: 68mm Length between blade mounting centers: 55mm Inner mounting diameter: 8mm COMMENTS: See propeller blades for assembly instructions. Sailplanes have no landing gear, and therefore would break a rigid propeller when the plane came in for a landing. The folding propeller folds back upon landing. The use of this hub will shorten the overall diameter of the prop by 10mm from the manufacturer"s length listing. wm 8/20/04