Attwood 5/16in Diameter Primer Bulb Gas Motor Accessory - Attwood's multi-layer primer bulbs provide the absolute best combination of performance, reliability, safety and compliance to ensure your experience on the water is easier and safer to enjoy. Attwood's exclusive three-layer design resists collapsing and hardening and ensures high output in temperatures ranging from 18degF to 122degF. Includes high-efficiency check valves with Viton O-rings for improved sealing. Assembled with the same components as Mercury and Quicksilver. * Exclusive three-layer construction provides the best spring-back during priming and excellent resistance to collapse during high-flow engine operation * Premium materials give the absolute best combination of performance and reliability * No cracking/hardening over time * Low permeation for EPA/CARB compliance * Excellent priming in extreme cold and hot environments * Zero chance of material delamination as seen by some competitor's products New high-performance check valve O-rings provide 30% improved priming while keeping optimized ow during engine use