Importance of cylinder sizing
Proper cylinder size is important to allow you room to grow, for pumping comfort and achieving an airtight seal. Choose a cylinder too small and you won't have any room to grow. Choose a cylinder too big and "scrotum suck" will diminish comfort and it will be harder to achieve a seal. The perfect size for you balances room, comfort and sealing capability.

"Scrotum suck" is an unwanted effect when using a 1st expansion cylinder - it occurs when penis pumping with too much space inside the cylinder. What happens is the scrotum on the outside of the cylinder gets sucked on the inside of the cylinder to fill up the empty space. The testicles then begin to smash against the outside walls of the cylinder causing discomfort. There are ways to avoid scrotum suck and selecting a proper size cylinder is the best way.

Measuring the penis for cylinder sizing
The following measurements must be taken while ERECT.

Circumference Measurement for sizing
This method is the easiest since it takes the guesswork out of sizing. There are two ways that I'd recommend.

Using fabric ruler
To measure using this flexible ruler around the largest part of your erect penis and note the measurement. This is your circumference.

Using string, pen & straightedge
To measure, wrap a string around the largest part of your erect penis and make pen marks on the string where it intersects one another. Straighten the string out against a straightedge ruler and measure the distance between the two points. This is your circumference.

Once the circumference is known, refer to the chart below to find the best size for you!

1.00" to 4.00"
Circumference

Small to Average