Features Pack of 4 Dimensions: 56mm x 34mm Durometer: 99A Pro Model: Dakota Servold Street Tech Formula Bones Street Tech Formula powers the legendary Bones STF wheels that roll fast, grip when you need to and slide when you want to, without flat spotting. STF gives you more control to skate with confidence. Bones STF wheels outperform all other wheels, and because they wear so well, they last several times longer than normal wheels, making STF wheels the best for less. Bones STF wheels are available in the original 103A and the new 99A Easy Streets for greater roll, control and softer landings on rougher terrain.