That is, the material is optional! Runs neither inwards nor outwards! Perfect brake pedal feel! Perfect braking! I used to use encoders - cylinders from A1-Cardone, after direct installation expansion tank - seals leaking! I installed an ACDelco brake master cylinder in a 97" Chevrolet Silverado K1500, great! Shipping from the USA to Germany is also very convenient! Thank you very much!