Sunlite Seatpost Clamp 34.9 Alloy Black

To Check For Sizing: Look On The Seatpost, Many Manufactures Will List The Sizing On The Post. 

Measure Outer Diameter Of The Seatpost. The Most Widely Used Sizes Are 34.9, 31.8, And 27.2 And All Are In Millimeters. 

The Inside Of The Seatpost Tube Will Measure Very Close To The Outer Diameter Of The Seatpost. The Outside Of The Seat Tube Will Of Course Be Larger But Can Give You A Reference Point For One Of The More Common Sizes Above.