Finally, a chain tensioner that meets the stringent NJS standards! For any product to be used in Professional Keirin racing in Japan it has to be "NJS" certified. <br /><br />This compact chain tensioner may be small but it is top quality. Do to the ingenious use of a double-threaded screw, it adjusts from 1cm in reach all the way up to 3cm. New design uses a 3mm Allen wrench! Fits drop-outs up to 5mm thick. Although designed for Racing, the ease of use makes this perfect for fixed gear road bikes. Sold in pairs. Made in Japan by Mikashima ( MKS). <br /><br />Don't settle for those ugly BMX-type adjusters... get MKS!