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At the moment golf clubs have a minimum length of 18" and a maximum length of 48", but there is an exception on the maximum length for putters. I am sure that 38" would be long enough for anybody with a non anchored style of putting.How long..?
A player of 5' would potentially need a putter of 30" but a player like Robert Karlsson plays something like a 37" putter but it looks like a normal size.
There's already a maximum length of a club isn't there..?
As long as the putter is held in the hands and you have to swing it, length isn't issue.