Support Ring Set for 3811A Portable Hardness Tester. Support Ring Set for 3811A & 3810A. Set Consist of: 1pc Universal Stand plus the following: Concave Support Rings: 11-13mm round, 12.5-17mm round, 16.5-30mm round, 11-13mm square, 12.5-17mm square, 16.5-30 square, Convex Support Rings10-15mm round, 14.5 ", 30mm round, 10-15mm square, 14.5" - 30mm square, 25-50mm square. Accessory Support Ring Set.