RetroArms Stainless Steel AOE Shim 3 mm for Piston Head

The RetroArms stainless steel spacer corrects the angle of engagement (AOE) between the sector gear and the piston. Installed between the piston head and the piston body, it shifts the piston back so that the first tooth of the sector gear engages the rack at the correct, nearly perpendicular angle.

The right thickness depends on the combination of piston, piston head and gearbox: 2 mm is the most commonly used size, 2.5 mm is for larger corrections and 3 mm for major corrections. A trial fit is recommended before final assembly, along with checking the full piston stroke and the air seal before closing the gearbox.

Benefits

• Removes the load on the first piston tooth, the main cause of its breakage
• Reduces the risk of tooth skipping in high-power or high rate-of-fire setups
• Extends the life of the piston and gears

Features

• Material: stainless steel
• CNC machined
• 3.3 mm countersunk center hole for a flat-head screw
• Reinforced version of the POM AOE shim: does not compress or deform under load
• Compatible with most pistons and piston heads (minor adjustments may be needed)

Specifications

• Thickness: 3 mm
• Outer diameter: 17 mm

Technical note: AOE correction should always be combined with a sorbothane damper on the cylinder head, and the air seal (nozzle length and piston stroke) should be rechecked after installation.