In some sealing applications the use of the standard design 76.90H / 76.97H is more complicated because of functional, constructive or production related reasons. This is the case, for example, when the seal type 76.90H / 76.97H is fitted into cylindrical bores. The adapter ring also facilitates a quick repairing possibility, e.g. for maintenance of coal mining machines direct on-site below ground. Therefore, a laborious disassembly and delivery of the parts to the workshop for refinishing is not necessary. In many cases, such initial problems can be solved fairly easily by using adapter rings type 76.91, which afterwards enable the standard seal to be fitted. The adapter rings are available in two forms, A and B, consisting of deep-drawn sheet metal casings sheathed in an oil-resistant elastomer material. The rubber-like, ribbed profile of the outer surface ensures static sealing and transmission of torque and protects from corrosion.