Sanyo provided these microphones with certain boombox models such as the M9994 and M9998 in the late 1970s. They include swivel stands that fit into slots on top of the boombox. Other boomboxes with these slots include the MX720, MX820, MX824, MX920, MX960, M9965, M9975, and possibly others.
The left and right mics actually have 2 different part numbers. This is because one of them (the HM-940) has an on/off switch, while the other one (the HM-941) does not. The one with the on/off switch has a special 2-prong jack wtih a remote activator that allows you to turn on your tape deck using the on/off switch on the mic. You can see on the side of your boombox there's a word "Remote" where that jack is supposed to go in. The other mic (the HM-941) just has a single 2.5mm jack like most other boombox mics.
I have seen two versions of these mics, one with silver Sanyo badges and model number badges, and the other with black Sanyo badges and model number badges.
