3 jaw and 4 jaw Chuck sizes

[Just for fun]

It seems that the standard 3 jaw chuck for 12x36 lathe is the 6" but yet the standard 4 jaw is an 8". Why is that? Why are both chucks not 8".

 

[Nutfarmer]

Lots of times when a 4 jaw chuck is used it is to center a casting or an odd shaped part. The larger size is helpful in this situation. It does depend on what your are working on

 

[Dabbler]

It seems that the standard 3 jaw chuck for 12x36 lathe is the 6" but yet the standard 4 jaw is an 8". Why is that? Why are both chucks not 8".

My 12X37 lathe has both chucks large: 8.25" for the 4Jaw, and 7.875" for the 3 jaw. 'Came that way from the factory.

 

[Just for fun]

.......

 

[jwmay]

Without dwelling too much on the existence of two identical threads, I would say that the only reason anyone could give you now is that it’s always been that way.
None of us but one has even been in sales or distribution of lathes at scale(that I know of). Reminds me of the story of the woman and the thanksgiving ham. But that’s too long a story to tell.