The new range of extensions have evolved from our well proven T-Series. They have been designed to offer distinct fit options. We have also adopted a new naming system whereby the name gives the angle material of teh extension. Thus 4525a is a 45 / 25 bend in aluminium. Performance The sole purpose of extensions is to provide a comfortable position for the riders hands relative to the armrests. They enhance performance by allowing the rider to relax into their optimal position. Which is why we provide different fit options so each rider can chase their best performance.