Street Tech Formula™ (STF) is specifically engineered from top quality components to obtain all the best properties necessary for the ultimate in street wheel performance. BONES® WHEELS has created a wheel with a substantially higher rebound for more speed and amazing slide capabilities while maintaining a resistance to flat spotting well beyond any standard wheel. The technology behind STF is proven. The results speak for themselves. About DUROMETER B SCALE Shore Durometer A Scale is good, but it does not cover the entire range of skate wheel hardness and is very limited because the scale goes from 1 to 100 and anything over A 95A does not compute accurately. Shore Durometer B Scale is perfect for skate wheels because: It is very similar to the A Scale, but reads 20 points lower, allowing the useful scale to be extended by 20 points, which covers the entire hardness range of skate wheels in one scale. It uses the same soft spring as the A Gauge, but the conical gauge needle of the D Scale. Because the spring is soft, the B Scale gauge needle does not puncture the skin of the wheel surface, resulting in the same reliable reading as the A Scale does.