Schaefer blocks have been manufactured in the United States since 1966 and are known for their legendary strength. Blocks are made from 316 stainless steel and hard coat anodized 6061-T6 aluminum alloy while the sheaves are made of UV protected Delrin. Schaefer offers the widest range of products for building block and tackle systems. Spring loaded blocks offer a wide flexibility in sheeting angles allowing for up to a 45 degree lead variation to each side of the track. "Spring Cap" design fully supports blocks under any conditions.