Spears Racing EX250 oil pump relief spring: 1.5kg /3.3lbs. of oil pressure at 4000 rpm with the OEM Relief spring.The new Spears Racing spring we got 3.8kgs/8.37lbs. of oil pressure at 4000 rpm.This Custom spring has been reset to produce greater pressure. The spring does not require specific shim just reuse the OEM washer with the clip as per manufacturer procedure. Spring is made of Carbon & Exotic steel that give a yellowish color.