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На английском, но всё понятно.

Notes on Mono Records & Cartridges Styli

Modern Microgroove Records have a V profile Groove & Modern Mono Microgroove Re-issues

0.7mil is Suitable for Reissue Monaural LP and a Mono LP of after 1960.
1.0mil is Suitable for the Monaural LP of a deep groove of the first press of the 1950s.
However, both styli can trace the monaural LP of all generations without a problem.
When you listen to the monaural LP of all generations, we recommend 0.7mil.
When you listen to a monaural LP of the first press of the 1950s mainly, we recommend 1.0mil.

3.0mil usually ideal for 78rpm mono records

Why Mono ?
A mono cartridge is mechanically different from a stereo cartridge. Simply switching a stereo cartridge to mono does not work perfectly. Despite what manufactures claim mono switches invariably add the two channels by simply shorting the two channels together, even very" expensive units do this. Hiend units can sum the two channels with extra electronics to eliminates the vertical response and improve the signal to noise by 3dB. However even summing does not provide the ultimate, a cartridge designed for mono, with a single coil and no vertical movement reduces surface noise, vertical noise and fits the groove properly.

Older Mono records have a U type Groove Mono/78RPM 3.0mil is the accepted norm & Steel Needles for gramophone records

other types used by collectors are 2.0/2.5/3.0/3.5/4.0/8.0 ( MIL = 1/1000th of a inch )

2.0MIL - 2.0 X 0.4 mil Elliptical diamond - worn LPs, some transcriptions.
2.5MIL - 2.5 X 0.5 mil elliptical diamond - late unworn 78s
3.0MIL - 3.0 X 0.5 mil elliptical diamond - most 1905 to 1940's, slightly worn 78s & transcriptions, & some Edison discs.
3.5MIL 3.5 X 0.8 mil elliptical diamond - old or worn 78s, transcriptions.
4.0MIL 4.0 X 1.0 mil elliptical diamond - Edison Diamond & very old/worn discs, raw aluminium, RCA home recordings., also Pathé vertical discs
8.0MIL 8.0 mil conical sapphire - RCA home recordings, and worn Pathé vertical discs.