Gear ratios and Gear box length: 
17.8mm gear bpx length based on gear ratios: 1/10
21.5mm gear box length based on gear ratios:1/20 1/30 1/45
24mm gear box length based on gear ratios:1/50 1/60 1/70 1/90 
26.5mm gear box length based on gear rations: 1/120 1/150 1/210 1/270
29mm gear box length based on gear rations: 1/450 1/540 1/630 1/810 

Technical performance:
MBI-37B555-10-12490
Gear ratio: 1/10
Voltage range:3-12V
Working voltage:12V
No load speed:490r/min
No load current: 0.4A
On load:1.7kg.cm
On load current:1.3A
On load speed: 450r/min
Stall torque:11.0kg.cm
Stall current:7.8A

MBI-37B555-30-12170
Gear ratio: 1/50
Voltage range:3-12V
Working voltage:12V
No load speed:170r/min
No load current: 0.4A
On load:0.44kg.cm
On load current:1.3A
On load speed: 150 r/min
Stall torque:28kg.cm
Stall current:7.9A

Applications: 

Robot, Curtain,Projector,Fingerprint Lock, Padlock, Vending Machine