Sterling's best selling friction hitch and autoblock has been redesigned with stronger aramid fiber. The 6.8 mm HollowBlock2 is made of 100% Technora® fiber for increased abrasion resistance and improved durability. It's gripping ability comes from the unique hollow-braid construction, for use as a prusik or Klemheist knot on ropes 7 mm or larger. 100% Technora Construction