In the "old days", it was widely known that using a mono cartridge on a stereo LP was verboten or at best ill-advised. Some vintage early stereo LP album covers even have that warning printed on the back, in fine print at the bottom right of the text. This warning is consistent with the concept that a (vintage) true mono cartridge with very low vertical compliance might potentially damage the groove walls of a stereo LP, which encode musical information in the vertical as well as the horizontal direction. Whereas mono LPs produce no musical signal due to vertical deflection of the cantilever. In those days, many if not most audiophiles owned mono cartridges as their main standby, so it made sense to make sure that those converting to stereo ought to use caution. Clearthink's sarcasm and bad manners are not at all justified. Not that such nastiness is ever justifiable on this forum.
However, in the modern era we have a plethora of new mono cartridges, only a few of which can be said to be "true mono". Miyajima mono cartridges are some of a very few such cartridges available. Most other recent production "mono" cartridges are actually stereo cartridges within which the channels are bridged one way or another to produce a mono output. Such cartridges are likely to have decent vertical compliance, unless they have been radically revised from their stereo origins, and such mono cartridges are not likely to damage a stereo LP. Whether or not a Miyajima mono (or any of the few other true mono cartridges) can damage a stereo LP, I do not know. But Robin Wyatt would know.
