Sprinco supplied inserts and O-rings to OEM clients for years. After failing to locate a supplier for true "Mil-Spec" components of consistent quality, they sought out top tier injection molding vendors, bought their own molds, and now supply their proprietary solutions that not only meet, but exceed the true current Mil-Spec performance requirements at a great price. Don't be short changed by US Commercial Grade hardware store or foreign imports of questionable heritage and/or compromised material composition. Everything Sprinco supplies is Made in the USA from superior grade base materials. Black Extractor Spring Inserts per MIL-PRF-6855-REV G Viton CRANE Mfg: Sprinco Usa