Siemens SINUMERIK User Manual page 201

Explanation of the parameters
DIATH (nominal diameter)
Use this cycle to perform thread undercuts for metric threads from M3 through M68.
If the value programmed in DIATH results in a final diameter of <3 mm, the cycle is aborted and alarm:
61601 "Finished part diameter too small" is issued.
If the parameter has a value other than specified in DIN76 Part 1, the cycle is also canceled, generating the alarm:
61001 "Thread lead defined incorrectly".
SPL (starting point)
The finished dimension in the longitudinal axis is defined using the parameter SPL.
FORM (definition)
Thread undercuts of the forms A and B are defined for external threads, form A for standard run-outs of threads, and form B
for short run-outs of threads.
Thread undercuts of the forms C and D are used for internal threads, form C for a standard run-out of the thread, and form D
for a short run-out.
See the following illustration for Forms A and B:
See the following illustration for Forms C and D:
Programming and Operating Manual (Turning)
201
01/2017