Pull start, square, 4-Bolt, Yimatzu Edition. Most commonly used for (but not limited to) 39cc, 47cc, 49cc pocket bikes, pocket dirt bikes, mini quads, mini scooters and standup scooters. Often referred to as a recoil.
 
Dimensions are 8.3cm square by 3.5cm wide. Mounting holes are 6.7cm apart centre to centre and are 5.8mm in diameter.