9.50MM LENGTH "METRIC POT"

The term "Metric" refers to the width of the threading. These Pots are commonly used in non U.S guitars as other countries use the Metric System. It is thinner in diameter than your standard U.S 3/8th pots

M8 THREAD OR 7.8MM WIDTH

3/8TH LENGTH "SHORT SHAFT"

The term "3/8th Shaft" refers to the length of the threading. 3/8th Pots are commonly used on Flat top guitars or guitars that have had their thick top routed to allow for the shorter shaft. These pots are also common when converting Metric guitars to U.S.

3/8TH WIDTH

3/4TH LENGTH "LONG SHAFT"

The term "3/4th Shaft" refers to the length of the threading. 3/4th Pots are commonly used on curved top guitars. The term "Curved Top" means guitars that have a thick "Curved" top that requires a lot of threading to poke through. Think Gibson Les Paul Standards.

3/8TH WIDTH

The difference is subtle but distinct. As the length of the threading is similar to each other, you can easily put Metric pots into U.S spec 3/8th guitars. But where the difference starts is you can not put 3/8th pots into Metric guitars. That is without Modding. As you can see from the above photo the difference between the 2 pots is the width of the shaft. 3/8th (In the Red) is wider than the Metric 7.8MM (In the white) so without enlarging the stock Metric holes it won't go through.

 The difference is distinct as the length of the threading on the 3/4th pots is double that of the 3/8th. As said above most guitars with a curved top use 3/4th pots and guitars with flat tops use 3/8th pots. If you are not sure which length your curved top guitar uses, it's always a safe bet to get the 3/4th length as you can adjust the threading with the nuts & washers to convert the 3/4th to 3/8ths. Another easy gauge is Les Paul’s with curved tops Pre-1977 use 3/8th and Post-1977 Use 3/4th!