The Rob Allen rubber is manufactured by a dip processing routine. While costing a little more than the average rubber, this enables fewer additives to be used which enhances performance on the guns. The coloured outer layer increases protection from the environment and the amber inner core is what gives you that trademark performance that Rob Allen products are known for. The 16mm is generally for 7mm-7.5mm spears. The majority of guns will come standard with a 16mm rubber, however they can all be upgraded for more power. Adding a second 16mm rubber on to your gun to have twin rubbers will increase your shooting power and allow you to penetrate through thicker fish.