The calculator
Runs in your browser. Inches or millimetres at the top.
How the grip number works
AC 43.13-1B paragraph 4-57 describes CherryMax rivets in four nominal diameters, 1/8, 5/32, 3/16 and 1/4 inch, plus oversizes, with universal and countersunk heads. For the Bulbed Cherrylock it notes that “their lengths are measured in increments of 1/16 inch. It is important to select a rivet with a length related to the grip length of the metal being joined.”
Reading the part number. CR3213-4-03: CR3213 universal head (CR3212 is the 100° countersunk), -4 the diameter in 1/32 in (1/8 in), -03 the maximum grip in 1/16 in (3/16 in). Distributor data sheets list -03 as 0.126 to 0.187 in: each grip number covers one sixteenth, up to its maximum.
So the grip number is the stack in sixteenths, rounded up: a 0.150 in stack is 2.4 sixteenths, grip -03.
Worked example
Two sheets, 0.063 + 0.090 in, measured 0.152 in through the hole, 1/8 in universal head.
- 0.152 × 16 = 2.43, rounded up: 3.
- Grip -03 covers 0.126 to 0.187 in; 0.152 is 0.026 in from the nearer end.
CR3213-4-03.
Limits — when NOT to use this
- The manufacturer's installation data governs, including the grip gauge to use, the hole size and the tooling. This tool reads the numbering only.
- Other blind fasteners (Cherrylock, Olympic, Hi-Lite) number their grips their own way.
- Approved data decides whether a blind rivet may replace a solid one at all.
Questions people actually ask
My stack is exactly 0.125 in. -02 or -03?
0.125 in is the top of -02 (0.063 to 0.125 in). On a limit, measure with the manufacturer's gauge and follow its reading; the calculator flags anything within 0.010 in of a limit.
Sources
- FAA AC 43.13-1B CHG 1, Chapter 4, par. 4-57 (blind rivets) — CherryMax diameters, heads and oversizes; Bulbed Cherrylock lengths in 1/16 in increments, selected to the grip.
- Distributor data sheets for CR3213 (e.g. Military-Fasteners, Boeing Distribution) — grip ranges per dash number, e.g. -4-03: 0.126 to 0.187 in. Not Cherry's own catalogue, which we have not yet read.