Made of natural rubber, Rubber content is not less than 50%, One-time shaped technolgy, ... 1. 4-1. 5mm, ID of the neck ≥18mm 4. Rubber content is not less than 50%, It was ensured that ... ageing ≥425%, measured elongation at break after immersion ≥425%. 5. Rubber hardness of washer is between 55-80 IRHD. Compression set ...