Each type of Hansen Patent I gear unit is designated by a number of three digits, except for size 1000 which is designated by a number of four.
In certain types, the numbers are preceded by the letter "D", "K", or "G" and/or are followed by letters "C", "T" or "CT".

Significance of these numbers and letters is as follows :

- The last digit designates the fundamental assembly, of which there are nine :

• horizontal parallel shafts	001
• vertical parallel shafts	002
• horizontal right-angle shafts	003
• right-angle shafts with vertical low speed shaft	004
• motor reducer with horizontal flange motor & horizontal shaft	005
• motor reducer with vertical flange motor & vertical shaft	006
• motor reducer with vertical flange motor & horizontal shaft	007
• motor reducer with horizontal flange motor & vertical shaft	008
• torque arm shaft mounted reducer	009

- The middle digit gives the number of reduction stages incorporated in the unit

- The first digit (or in case of 4 digit number, the first two digits) designates the size of the unit. There are 10 sizes designated respectively by the figures 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

- "D" : always precedes the number and indicates a centerline split unit

- "G" : this letter also always precedes the number and signifies a multi-speed gear unit

- "K" : always precedes the number to indicate a right-angle gear unit

- "T" : follows the number and signifies that certain gears incorporated in the gear unit have surface hardened teeth

- "C" : follows the number and signifies that the speed reducer is equipped with double helical gears of opposite hand to form herringbone gears