ND question

[rollfaster]

Ok. Just kinda wandering what year ND stopped using split sprockets? I have two example here: earlier one with split top pic and no split on bottom. No real issues here, just curiosity. Both are 1/2” 20t.

 

[island schwinn]

I have an original 53 and 54 bike.53 is split, 54 isn't.

 

[Gordon]

It is my understanding the slot was so you could change a spoke without removing the sprocket. I also heard or read that the guy who came up with the idea never got a penny for his invention. As to when they were discontinued, I have no clue.