A fastener counting machine counts screws, bolts, nuts, washers and rivets piece by piece, usually with cameras, so every bag, box or kit holds the exact quantity. Unlike a counting scale, it does not depend on piece weight, which changes with plating, material and lot. Drop zone counters count small fasteners at hundreds of parts per second; larger parts such as ¼-20 nuts count at about 200 per second.
This article is part of our complete guide to automated counting. Here we look at what makes fasteners hard to count accurately, how a counting machine handles each type, and what to check before you automate.
Why fasteners are hard to count by weight
Most fastener distributors and packers count by weight: weigh a sample, work out an average piece weight, then fill bags to a target weight. It is fast, but it assumes every piece weighs the same as the sample, and fasteners often do not.
- Plating and coatings such as zinc, cadmium or thread lock add weight that varies from lot to lot.
- Material changes between steel, stainless, brass and aluminum change weight for the same size.
- Manufacturing tolerances on length, head size and thread vary between suppliers.
- Mixed lots combine parts from different runs with different average weights.
Worked example: how a small weight error becomes a short count
A packer counts 1,000-piece bags of screws by weight. The sample says each screw weighs 2.00 g, so a bag is filled to 2,000 g. The new lot has a slightly heavier plating and actually averages 2.04 g. 2,000 g ÷ 2.04 g = 980.4 screws, so every bag is about 20 screws short, a 2% error that nobody sees until the customer counts. To avoid that, packers overfill, and the overfill is given away on every bag.
A counting machine removes the problem because it never uses weight. Our comparison of counting scales and counting machines goes deeper on when a scale is still good enough.
Counting each type of fastener
| Fastener | What makes it tricky | How a counting machine handles it |
|---|---|---|
| Screws | Varied lengths and head styles; they roll and tumble | A drop zone counter images each screw from two views, so screws that cross or overlap are separated |
| Bolts | Larger and heavier; fewer per second | Counted at lower feed rates for accuracy; larger standard and custom counters for long parts |
| Nuts | Uniform but heavy; can stack | About 200 per second for parts such as ¼-20 nuts on a drop zone counter |
| Washers | Flat parts that stack and nest | Feeding is set up to separate them so the camera sees each washer |
| Rivets | Small, light parts in large quantities | Counted at high rates; weight-independent, so light parts are no problem |
| Lock washers, clips and springs | Can tangle and hook together | Tested with samples first; feeding and orientation matter more than speed |
Standard Sciotex drop zone counters handle parts from 0.3 mm to 150 mm, covering most fasteners. The PerfectCount parts counting machine comes in three standard sizes, Mini, Standard and XL, matched to part size.
Speed and accuracy for fastener counting
| Measure | Typical figure |
|---|---|
| Top drop zone speed | Up to 2,000 parts per second for small parts |
| Larger fasteners such as ¼-20 nuts | About 200 parts per second |
| Accuracy at lower feed rates | Better than 99.99% |
| Accuracy at hundreds of parts per second | Above 99.5% for most parts |
For exact bags and kits, run at a feed rate that gives the accuracy you need, and set the gate so any rare error falls on the safe side. For most packers a rare single extra fastener is far cheaper than a short bag.
Where fastener counting machines are used
- Fastener distribution and packaging: bagging and boxing exact quantities instead of overfilling by weight.
- Aerospace and defense: fastener accountability, kit accuracy and foreign object debris (FOD) control, with a record of every count.
- Kitting for assembly: every kit gets the right number of each fastener, so assembly lines do not stop for missing parts.
- Inventory and receiving: verifying supplier quantities and counting returns quickly.
If counts are small and mixed, a benchtop counter can be faster than setting up a feeder: the operator spreads the fasteners, gets an instant count and sweeps them off. See BenchCount. For setting up a full counting and bagging cell, see how to automate bulk and batch counting.
Before you automate fastener counting
- List the fastener types, sizes and materials you count, and the batch sizes for each.
- Measure how much you overfill today and how often customers report short counts.
- Send sample parts, especially anything that tangles, nests or stacks.
- Decide where counts go: hand bagging, an automatic bagger, kits or inventory.
- Decide what records you need, for example per-batch counts for aerospace or defense customers.
Counting screws, bolts, nuts or rivets?
Sciotex designs and builds fastener counting machines, from standard drop zone counters to custom counting and bagging cells, designed, programmed, built and supported in the US since 1997.
Frequently asked questions
A fastener counting machine counts screws, bolts, nuts, washers and rivets individually, usually with cameras, so each package holds an exact quantity regardless of piece weight.
A counting scale estimates the count from an average piece weight. Plating, material and lot changes alter the weight, so bags end up short or overfilled. A counting machine counts each piece.
Drop zone counters reach up to 2,000 parts per second for small parts. Larger fasteners such as ¼-20 nuts count at about 200 per second.
Yes, with the right feeding. Washers can stack and springs can tangle, so samples are tested first to make sure the parts reach the camera one at a time.
Standard Sciotex drop zone counters handle parts from 0.3 mm to 150 mm, which covers most screws, bolts, nuts, washers and rivets. Larger parts can be counted with custom systems.
Related articles
- Automated Counting: The Complete Guide to Industrial Counting Systems
- How to Automate Bulk and Batch Counting of Small Parts
- Counting Scales vs. Automated Counting: Which Is Right for You?
- Manual Counting vs. Automated Counting: Cost, Errors and How to Switch
- Electronic Component Counting: Connectors, Terminals and Loose Parts
