When combined with the K-Pact or the K-Pact zip this small item converts our knee pads into full-guard knee-shin-combos. Not sure if you need a knee pad with extension or without? Well, go for the Pacts, add the S-Pad Amp and stay flexible. HD_Memory_Foam adjust to your shin for the best protection. You can find the right size by choosing the same size you wear on the K-Pact/K-Pact Zip. The S-Pad is 26.5cm long in all sizes. The circumference is based on the size of the K-Pact/K-Pact Zip and can be adjusted at the bottom using a Velcro strap.