Description : This is an indispensable shop tool that can be used to both measure and straighten misaligned derailleur hangers solving a high percentage of shifting problems . Simple to use : The Derailleur Hanger Alignment Gauge can help solve a multitude of derailleur shifting problems , most notably with index shifting systems . This tool is extremely steady in operation . The tool threads directly into the derailleur hanger . The gauge bar holds a gauge which marks the distance to the wheel . The gauge then is rotated with the wheel to the 3 , 6 , 9 , and 12 o &# 39 ; clock positions , noting any differences in measurements . The alignment of the derailleur hanger is accomplished by applying pressure to the tool &# 39 ; s arm . The results can be checked instantly . Gauge bar made of High - strength aluminum alloy , Hardened by heat treatment . Adjusts to fit 20 & quot ; to 29 & quot ;+ wheels . Replaceable threaded tip . Upgraded large inner shaft for added strength . Tighter tolerances for improved accuracy . Improved clearance and reach to fit more frame / hanger combos including low clearance thru - axle derailleur hangers . Specification : Material : aluminium alloy Package Size : 27x14x4 . 5cm / 10 . 63x5 . 51x1 . 77inch Package Includes : 1 Piece Black Derailleur Hanger Alignment Gauge HAG - 3 1 Piece Red Derailleur Hanger Alignment Gauge HAG - 3