Mercruiser Alpha I U-Joint Bellows with Ridge | Sierra 18-2751 Sierra 18-2751 U-Joint Bellows For Mercruiser Alpha I, R, MR, TR and TRS stern drives from serial number 3469428 and up with ridge. Mercruiser Alpha I U-Joint Bellows With Ridge For Mercruiser Alpha I, R, MR, TR and TRS stern drives from serial number 3469428 and up with ridge Stainless steel clamps included Replaces Mercury 60932A4 Replaces OMC 775540 Replaces Mallory 9-72701