Mirage Cycling Innovations Chain Tensioner 2 pack. 
16mm adjustment with 2 x 10mm mounting holes. Constructed from 7075 aluminium. Fits most frames for use on any open ended rear drop outs.  Easy to install. When used correctly Mirage Chain Tensioners will protect your frame drop outs and hold your rear wheel in place perfectly. Available in red, gold, silver and black with laser etched logo graphic.
Weight: 34g each - total weight 84g.