An EFR retainer (+0) is measured from the top of the outside where the gripper meets.
Pictured (L to R) Gripper, +40mm, +20mm and +0 retainer)
The +40mm is 55mm from the base to top of bell. (just below the gripper backstop)
Depending on how one wants to measure, you can add 15mm to the number listed.
Available in sizes +0, +5, +10, +15, +20, +25, +30, +35, +40, +50, +55, +60, +65
