These 3-12V Gearmotors are great for many different applications. Measuring 37 mm (1.45?) in diameter, they are a good size for robotics, r/c and other mid-size projects. Offered in a range of gear ratios from 10:1 to 3000:1. These motors have a .715” long 6mm D-shaft and are compatible with 6mm bore gears, sprockets, couplers, etc. The gear train is a metal / plastic combination providing strength and durability. Other features include: solder type terminals, an oil-bearing design, and a dielectric Strength of 300VDC. If you’re looking for a quality and affordable motor solution, these are your best bet!