Many Semi-Professional lathes (Rek-O-Kut, Presto, etc) used an interchangeable feedscrew stystem to determine width of space between grooves, and therefore, the amount of cutting time possible per side.

"Coarse" Feedscrews - Some feedscrews had very large threads, and generally started at about 88-136 lpi (lines per inch). 
"Fine" Feedscrews - Feedscrews went up to approximately 186-256 lpi.

"General Use" Feedscrews - Feedscrews in the range of 144-180 are considered to be pretty general use feedscrews and allow for reasonably full volume recordings with a reasonable amount of time per side.

Inside Out Feedscrews - Feedscrews that cut from the middle of the record to the outside edge were also made.  These allowed cutting without a vacuum system, as the chip/swarf tends to trail out towards the middle of the disc.

The louder and bassier the audio, the coarser the feedscrew needs to be, because the grooves have to be further apart, as the groove moves laterally based on the volume and bass.

To calculate available time with each screw use this formula:
Amount of cuttable space on a record (measure the amount of groove space on one half of a record: 2" on a 7" or 3.5" on a 12") * LP1 / 60 (seconds).

i.e. - A 7" record using a 144 lpi feedscrew would be:

(2*144)/60 = 4.8 minutes of cutting time.

Below is schematic for Outside-In Feedscrew for Presto 6N.