I bought this for the rear 40mm bearings on my 2013 Rzr 800s. Front bearings 44mm. Had to replace the rear bearings and used this new tool to lubricate the new bearing once installed. The new bearing took another 10 pumps for lubrication to appear. Very easy to use, just remove the brake caliper, axle split pin, axle nut (27mm head) and wheel hubs. Now place the tool on the axle in the bearings and pump the tool until you see the grease start to flow. with water (warehouse repacking is used) that was in the warehouses and stop. If you keep pumping, you can blow the seal. This tool extends wheel bearing life. Be sure to use a good quality marine lubricant. Don't buy cheap wheel bearings.