Well, the Thomson Elite comes in:

25.0mm
25.4mm
26.0mm
26.6mm
26.8mm
27.0mm
27.2mm
27.4mm
28.6mm
29.4mm
29.8mm
30.0mm
30.6mm
30.8mm
30.9mm
31.4mm
31.6mm
32.4mm

As to yours, the diameter and length is often stamped near the bottom of the post, on the part that resides inside the frame.