This is a Vortech 4-1/2" Aluminum Big Cut Two-Blade Spinner from Dave Brown. FEATURES: Light-Weight Aluminum Construction Polished, Brushed Aluminum Color Includes Four Plastic Backplate Bushings, So The Backplate Will Fit Securely Around Any Ordinary Crankshaft Designed for Two-Bladed Props INCLUDES: One Two-Blade Aluminum Spinner (For Sizes See SPECS) One Aluminum Backplate One 10-32 x 2" Cap Head Mounting Bolt Four Plastic Backplate Adapter Bushings One Instruction/Information Header Card REQUIRES: Vortech Adapter Nut (See COMMENTS) 4mm or 5/32" Allen Wrench (For The Cap Screw) SPECS: Spinner Backplate Diameter: 4-1/2" (114mm) Spinner Backplate Thickness: 3/16" (4mm) Spinner Backplate Hole Diameter: 3/8" (9.5mm) Length From Back Of Backplate To Front Of Cone: 4-1/2" (114mm) Weight: 7.5 oz. COMMENTS: To Attach the Spinner to the Engine, the Modeler Must Use One of the Following Adapter Nut Sets. This spinner uses a LONG adapter Note: Use A Short Adapter With Spinners 2-1/2" And Smaller. Use A Long Adapter With Spinners 2-1/2" And Larger. Use A X-Long Adapter With Spinners 3" And Larger. 1/4-28 DAVQ8428 (Short), DAVQ9428 (Long), OS Max .25-.60,R, Como .19-.61, Enya .25-.53,Fox .19-.50 HP .21-.61, Irvine .20-.61, K&B .19-.65, OPS .40-.60, Peco .21-.45, ST .25-.60, Webra .28-.80 5/16-24 DAVQ8524 (Short), DAVQ9524 (Long), DAVQ6524 (X-Long) OS Max .61-.90, Supertigre .61-.90, Fox .60-1.2 7x1.0mm DAVQ8710 (Short), DAVQ9710 (Long) Enya .35-.60, .60-1.2 Four Strokes (Non-R Engines) 8x1.0mm DAVQ8810 (Short), DAVQ9810 (Long) YS .90-1.2 4-Stroke, Enya 1.2R 4-Stroke, OPS Super .60 and .61 5-Port 8x1.25mm DAVQ8812 (Short), DAVQ9812 (Long), DAVQ6812 (X-Long) All YS 2-Stroke, OPS Maxi .30, Webra .61-1.2 nt 10/24/08 ir/jxs