The part in the gear selection mechanism that looks a bit like a bottle opener. The early Nordwests had a problem with a faulty batch of them. The symptoms were baulking when changing up, most often between second and third under heavy load. It certainly affected mine. Not very good for hill climbs.
When I took a trip to Milan on my road Nordie I picked up a spare from Motta, not far from FPM in Canonica d'Adda. Cured that problem completely and only requires the outer case to be taken off.
I supopose a lot of wear on the same part might lead to 'missing gears' rather than not changing up,if that's what's happening. Joachim might know more details.
"Do not adjust your mind, there is a fault in the reality"
1957 175 Sport