The four-bolt flange is a proven leak-free connection, especially suited for larger sizes. As a result, it has achieved worldwide acceptance. The connection's success is in its simplicity. It is a static face seal using a high durometer O-ring for the seal and clamps and bolts for the holding power. This simple design provides several advantages over threaded port connections, such as NPT, SAE, BSPP, ISO 6149, etc., in larger sizes: Ability to connect up to 5 inch O.D tube (code 61 only). Much lower tightening torque required from the four bolts compared to that required for equivalent size threaded port. Less tightening torque means smaller wrenches and wrench swing clearances - providing ease of assembly in tight quarters. Up to 6000 psi capability through 2" size (code 62 only). Single seal point between tube/pipe/hose assembly and the port. Ease of disassembly due to zero clearance with the port. The connection has one disadvantage - it requires a larger area (footprint) on the component than an equivalent threaded port. Parker offers over 30 different 4-bolt flange series and over 20 different flange head series. This represents over 1200 standard part numbers available to provide the best possible plumbing solution. The vast majority of our flanges are manufactured from forged steel with a limited amount machined from bar stock. The forged construction provides higher strength and durability to provide long lasting performance in the application. Parker flanges are designed to meet or exceed SAE J518 and ISO 6162. There are also designs available that were commonly used by some pump manufacturers but are not governed by any organizational specification.