The calculator
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How the weights are worked out
Weighed: the best figure. Put a counted sample on a scale, 20 pieces or more, and divide: unit weight = sample weight ÷ count. That is what a team does by hand with a table; here it takes ten seconds and carries through to the list. It is the only method offered for blind rivets, bolts and consumables, which have stems, sleeves, collars and packaging of different materials.
Solid rivets: an estimate by geometry. The shank is a cylinder, π/4 × D² × L, with L from the length dash in sixteenths. AC 43.13-1B Figure 4-4 measures it under a universal head and overall on a countersunk one. The universal head uses the FAA Airframe Handbook ratios, 2D across and about 0.425D high, as a spherical cap. The MS20426 head is a 100° cone from the shank to the mid-range head diameter. Densities come from MIL-HDBK-5J: 2017 at 0.101 lb/in³, 2024 at 0.100. 2117 (AD) is not in MIL-HDBK-5J, so the 2017 figure stands in for it.
Sheet is length × width × thickness × density, with MIL-HDBK-5J densities. Fabric is areal weight × area, with the areal weight taken from the fabric's data sheet.
Worked example
MS20470AD4-4: 1/8 in universal head, 1/4 in long, 2117.
- Shank: π/4 × 0.125² × 0.250 = 0.003068 in³.
- Head: D = 0.250 in, h = 0.425 × 0.125 = 0.0531 in; cap = π × 0.0531 × (3 × 0.125² + 0.0531²) / 6 = 0.001382 in³.
- Weight: (0.003068 + 0.001382) × 0.101 = 0.000449 lb each, about 2,225 per pound.
A 1 lb bag of AD4-4 holds roughly 2,200. Weigh 20 to confirm it before you count on it.
Limits — when NOT to use this
- Logistics, not engineering. For inventory, packing and ordering. It does not replace the IPC or the SRM, and it says nothing about which part to use.
- Geometry is an estimate. Real heads and tolerances differ; weigh a sample when the count matters.
- Dangerous goods. The flag is a reminder, not a classification. The product's safety data sheet, the IATA Dangerous Goods Regulations and the airline decide what can travel.
- Bag limits differ by airline and ticket. 23 kg is a common checked-bag limit; set your own.
Questions people actually ask
Why can't it calculate a CherryMAX from its number?
Because a blind rivet is a sleeve, a stem and a locking collar, often in different metals: a Monel sleeve weighs about three times an aluminium one. Without the manufacturer's weight per thousand, weighing a sample is the only honest figure.
How accurate is the count from a weight?
As good as the scale and the sample. With 20 or more pieces on a scale reading 0.1 g, the unit weight is within a few percent; the calculator shows ±5 % on the count.
Sources
- FAA AC 43.13-1B CHG 1, Figure 4-4 — rivet part number breakdown: diameter in 1/32 in, length in 1/16 in, measured from the top of a flush head and the underside of a universal head.
- FAA-H-8083-31, AMT Handbook — Airframe, Volume 1, Chapter 4 — universal head proportions, 2D across and about 0.425D high.
- MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures — densities: 2024 0.100, 2017 and 7075 0.101, 6061 0.098, 5052 0.097, 4130 0.283, Ti-6Al-4V 0.160, CP titanium 0.163, AZ31B 0.0639, Inconel 625 0.305 lb/in³.
- MS20426 head diameter limits, from distributor data sheets — mid-range head diameters for the countersunk geometry; no 1/4 in figure, so 1/4 in MS20426 is not computed.