7mm or 5/16"

Woody's 1993 Catalog

Woody's 2002-2003 Safety & Performance Trail Catalog (page 4)

3. Select the stud design and shank size (7mm or 5/16"), taking into consideration your riding style. The 7mm studs are smaller in diameter at both the head and shank, therefore lighter... These studs can be used on snowmobiles with a horsepower rating of 100 or less. The 5/16" studs have a larger head and shank... Sleds over 100 horsepower (600cc range) and performance riding are good benchmarks for a decision to use 5/16" studs.
 

1/4"    7mm    5/16"

Push-Thru Stud History                         Hot Tip Pro-Tracks Fast Trac Roetin Woody 1st Push-thru 1st 5/16"stud 1st stainless stud   1975 1975   1986   1991 1991 1991   1992 2002   1993 1995 2003

How much R&D can it take to beef up the shaft by only .020?

This shows that Fast Trac has been the leader, in providing studs that meet the demands of aggressive trail riders.