This is the 18.1x10 Composite Pattern Propeller from Advanced Precision Composite. FEATURES: Constructed of composite material For pattern applications INCLUDES: One 18.1x10 composite propeller REQUIRES: ALL props require balancing, this is VERY important, use TOPQ5700. May need prop reamer, use GPMQ5006 (SAE) or GPMQ5007 (Metric) SPECS: Diameter: 18.1" Pitch: 10 Hub inner diameter: 0.25" rmb 02-17-07 ir/jxs