Question: What is the customary way to call out ACME and Trapezoidal lead screws?

Answer:  It depends on the type of screw, as follows:

Single-Thread ACME Screws:  1-4-ACME-4C-LH x 144 indicates a centralizing class 4C ACME thread of 1-inch major diameter, 4 threads-per-inch, single-thread, left-hand thread and 144 inch overall length.  The hand designation is not required for right-hand threads.

Multiple-Thread ACME Screws:  1-0.25p-0.5L-ACME-4G x 144 indicates a general purpose class 4G ACME thread of 1-inch major diameter, 0.25 inch pitch, 0.5 inch lead, double-thread, right-hand thread and 144 inch overall length.  The number of threads or thread starts is determined by dividing the lead by the pitch.

Single-Thread Trapezoidal Screws: TR 20 x 4 LH x 3,660 indicates a trapezoidal lead screw of 20 mm diameter, 4 mm lead, single-thread, left-hand thread and 3660 mm overall length.  The hand designation is not required for right-hand-threads.

Multiple-Thread Trapezoidal Screws:  TR 20 x 4 (P2) x 3,660 indicates a trapezoidal lead screw of 20 mm diameter, 4 mm lead, 2 mm pitch, double-thread, right-hand thread and 3,660 mm overall length.  The number of threads or thread starts is determined by dividing the lead by the pitch.