Metal Disk...

[Electronic M]

I remember when I was a kid finding a similar disc in an antique shop and ruining the styli on a couple of phonos I liked only to get nothing but noise off the disc...I eventually got mad and bent it like a taco.

Wood needles were fairly common pre-war especially on windup machines and were available in a wide variety of materials from thorns to cut bamboo...The main purpose was to reduce volume on acoustic machines, but they could also change tonal characteristics and both electric and acoustic phonos used them for that.