The WP or wiper plunger has the highest amount of interference. This provides the most complete wiping action on the cartridge inside diameter. The P-plunger has medium interference. It provides clean wiping action, inserts easily, and allows evacuation of entrapped air. The PRS or pressure relief plunger has the least interference. It has been specifically designed to be easily inserted and reduce air entrapment during filling and dispensing. This dramatically reduces problems with dripping or stringing during dispensing.