ZE28W - Hydraulic 3-Jaw Coupler with Ball Check 1/8” NPT (F) 8,000 PSI is an accessory designed for dependable use with Goat Pumps fluid-transfer equipment and compatible setups. About This Item:. This 4-Jaw coupler was designed with professionals in mind and is used with a variety of grease gun types. With a maximum pressure rating of 8,000 PSI this grease gun coupler can be used with manual and electric grease guns alike.