There are two different types of ISO flange. Bolted flanges( F-type) have a set of bolt holes to allow flanges to be joined together. Fixed and rotatable bolted styles are manufactured. Claw clamp flanges (K-type) use demountable claw clamps to hold the two mating flanges together. The S.S. Centre ring with Viton O-ring is sandwiched between the two mating flanges. Fourvac also manufacturer and supplies the accessories like Centre rings, Viton O-rings and double and single claw clamps with high tensile Bolts and Nuts.