This is the Hot Racing Aluminum CNC Heavy Duty Servo Saver in Black anodize, with a heavy spring tension. 

Features:

• CNC 6061-T6 aluminum construction
• Black anodized
• Multiple inserts to accommodate many different servo splines

Specifications:

• Length: 1-1/2 inch (38mm)
• Diameter: 1 inch (25mm)
• 23 Tooth Insert (K): (KO, Sanwa, JR, Airtronics, Spektrum)
• 24 Tooth Insert (H): (Hitec)
• 25 Tooth Insert (F): (Futaba, Traxxas, SAVOX, Tactic, some of the new Hitec) 

Includes:

• (1) servo saver
• (1) spline adapters for 23 tooth (KO, Sanwa, JR)
• (1) spline adapters for 24 tooth (Hitec)
• (1) spline adapters for 25 tooth (Futaba)