The Stop Arm (also known as the Armature, Bell Crank, or Swivel Arm) is the piece that connects to the rotor shaft and moves the rotor back and forth. This screw holds it in place. -cdp
Specifically for these models and their variants. Other models may qualify as well:
Horns
• 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
• H378
• H379
• H602
• H650
• H651M
• H652M
• HNSOL100
• HNSOL200
• LB77
Trombones
• TR150 Tenor Trombone
• TR158 Tenor Trombone
• TR160 Tenor Trombone
• TR181 Bass Trombone
• TR183 Bass Trombone
• TR188 Tenor Trombone
• TR602F Tenor Trombone
• TR680 Tenor Trombone