Holton, French Horn, waterkey pin.
Fits:
77
77N
H105
H175
H176
H177
H178
H179
H180
H181
H188
H189
H192
H200
H275
H276
H277
H278
H279
H280-H280ERA
H281
H288
H289
H292
HNSOL200
LB77
TR690