This is the Spektrum H2026L 2.1 Gram Linear Long Throw Servo. This servo is a direct replacement for the Blade Nano CP X and mCP X BL helicopters and has a 38mm lead. 

Specifications: 
Size Category: Specialty 
Type: Analog 
Torque: 3.5 oz (100 g) @ 3.7V 
Speed: 0.10-0.14 sec end-to-end 
Length: 0.87 in (22.0mm) 
Width: 0.66 in (16.9mm) 
Height: 0.33 in (8.2mm) 
Weight: 0.1 oz (2.1 g) 
Bushing Or Bearing: Bearing 
Bearing: Single 
Motor Type: Brushed 
Connector Type: JST-SHR 1.0 mm, 38mm lead 
Gear Type: Nylon 
Voltage: 3.2–4.2V