This is the medium diameter axle peg - measuring 6 x 35mm - and is suitable for the following wheels (as shown in the first image) -
TW-1000 25mm Standard Wheels
TW-1500 38mm Standard Wheels
TWR-150 38mm Recessed Wheels
TWR-200 51mm Recessed Wheels
The installed shaft length is approximately 30.0mm long so to calculate the remaining peg that can be used once passed through the wheels, reduce this length (30mm) by the thickness of the wheel.
The axle pegs are bought individually and discounts are available for bulk quantities.