An Oil Seal (also known as a Shaft Seal, Lip Seal or Elastomeric Lip Seal), is a simple device for excluding dust, dirt, water or any other contaminant whilst retaining lubricant in rotary shaft equipment. Generally, Oil Seals have been developed as a means of protecting the bearings of rotating shafts.

R21 Oil Seals have a metal body which is rubber coated and contains a single sprung lip. R23 Oil Seals have an extra lip called a 'Wiper Lip', and are sometimes referred to as 'Double Lip'.

Thi is an R23 style seal with an ID of 20mm, an OD of 42mm, and a thickness of 8mm.