The extended centre distance STM gearbox from HMA Flow & Industrial is designed specifically for small- to medium-size power requirements. The result is a flexible and easy-to-install unit particularly suited for a range of applications such as screw conveyors, mixers, and travelling drives. Ratios from 17.2 to 1101:1 are available. The design of this gearbox series is based on a rigid monolithic structure to allow for heavy loads.

The parallel shaft gearboxes or shaft-mounted gearboxes and motor gearboxes have three or four stages. Model sizes range from a Size 25, with a 20 mm shaft diameter, to a Size 95, with a 55 mm shaft diameter, with either hollow-keyed or shrink-disc output. These gearboxes utilise standard IEC inputs, from IEC56 to IEC160, to allow for modular frames, with optional solid-keyed input as well as output mounting flanges.

Housings and flanges are manufactured in engineering cast iron (G20 UNI 5007), while Sizes 25, 45, and 65 are made from aluminium (SG-AlSi UNI 1706). All the housing machining is carried out in CNC work centres for maximum construction accuracy. The input shaft is made from case-hardened and hardened steel (39NiCrMo3 UNI 7845 or 36NiCrMo4 UNI EN 10083), while the output shafts are made from steel (C40 UNI 5332). All gears are made from steel (18NiCrMo5 UNI7846), previously case-hardened, or hardened and rectified, so as to boost efficiency and quietness, even under load.