A SOM stands for a secondary operation machine. There are three forms of Som's. The first is an H-SOM or hand operated operation, such as a pair of scissors or a knife for trimming. The second form is the gang secondary operation or G-SOM. This refers to gang type of finishing machines such as cutting boards, steel rule, CO2, tumbling, dry tumbling, and the Altman Gang Trimming Machines. The third form is the R-SOM, which refers to a rotary type of operation.

The design of an R-SOM requires many considerations, but the piece part is the first and most important. The part controls how it is to be handled. The first two considerations is how this part is going to be held during the rotary operation and how is it going to be unloaded. Sometimes there is a need to raise and lower the table or locating disc into which the parts are to be placed. The part can also be placed directly on to a post or slitter, and in this case extra care must be taken to protect the operator.