Screw Size Identifier: Find Any Screw by Measurement
You found a loose screw in a drawer. It looks like a few things you have, but none of them quite match. You need to know: what is it, and where do I buy more? This article walks through the five inputs our identifier needs and shows a full example — from rattling screw to ordering line.
How the Identifier Works
The tool uses a lookup of standard fastener tables (DIN/ISO metric, ASME UNC/UNF inch) and returns the closest valid size for your measurements. It accounts for manufacturing tolerance — a 5.97 mm measurement is correctly identified as M6, not M5.5.
What You Need Before Starting
- Diameter — measured across thread crests (mm or inches).
- Length — measured per the head-type rule (see How to Measure a Screw).
- Head type — flat, pan, round, oval, truss, bugle, hex, socket cap.
- Drive type — Phillips, slotted, square, Torx, hex, combi.
- Thread pitch — metric mm or imperial TPI.
Common Screw Types and Where They Live
- Wood screws — coarse, sharp threads partway up the shank, used in lumber and plywood.
- Drywall screws — fine bugle head, usually black phosphate, aggressive point.
- Machine screws — uniform threads full length, thread into a nut or tapped hole.
- Sheet metal screws — fully threaded, sharp self-piercing tip, for thin metal.
- Deck screws — coated for outdoor use, often square or star drive.
- Self-tapping — cuts its own thread via fluted tip; used in metal, plastic, or pre-drilled holes.
Identifying Without Calipers
Open the identifier on your phone and tap “Calibration Ruler”. The screen shows a ruler scaled to your device; you confirm by holding a credit card to the display. Lay the screw flat and read diameter, length, and count threads per centimeter to estimate pitch.
Sample Walkthrough
You pull an unknown screw out of a laptop’s back panel. It’s tiny, black, with a Phillips head. Measurements:
- Diameter: 2.98 mm
- Length: 5.0 mm
- Pitch: 0.5 mm (measured 10 threads = 5 mm)
- Head: pan; Drive: Phillips #00
Enter those in the identifier. Result: M3 × 0.5 × 5 mm pan head machine screw. Search that designation on any supplier site and you’ll get a 100-pack for less than a coffee.
Ambiguous Cases to Watch
Some sizes are close enough to confuse even experienced techs. Check diameter precisely:
| Looks like | Metric (mm) | Imperial (mm) | How to tell |
|---|---|---|---|
| M5 vs #10 | 5.00 | 4.83 (#10) | Pitch: M5 = 0.8 mm; #10 = 24 or 32 TPI |
| M6 vs 1/4" | 6.00 | 6.35 | Always check — 0.35 mm is measurable |
| M3 vs #4 | 3.00 | 2.84 (#4) | Caliper only; they never thread together |
Identify Your Fastener Now
Head type, drive type, measurements — in under a minute you have the exact designation and a shopping link.
Open Identifier →Recommended Tool
CLBDRESS Thread Checker — 50-Piece Kit
Male/female threaded samples from M3 to M16 and #4 to 1/2". Drop the mystery screw into a matching hole — instant size ID without a caliper.
View on Amazon →Frequently Asked Questions
What size screw is this?
Measure diameter across the thread crests, length per the head-type rule, and thread pitch, then enter those into the identifier. It returns the nearest standard size like M4 × 0.7 × 20 or #8-32 × 3/4".
Can I identify a screw without calipers?
Yes. Use the on-screen calibration ruler to measure within ±0.2 mm, pick the head and drive type, and the tool narrows it to the most likely standard size.
How do I tell M5 from #10?
M5 is 5.00 mm; #10 is 0.190" (4.83 mm). They look similar but a caliper tells them apart — and they use different thread pitches (0.8 mm vs 24/32 TPI) that will not interchange.
What information does the identifier need?
Diameter, length, head type, drive type, and thread pitch (or thread count). Grade and material are optional but help narrow results for structural applications.
Does the tool cover wood, drywall, and sheet metal screws?
Yes — the head/drive selector includes wood, drywall, self-tapping, deck, and machine screws as separate categories so thread geometry is matched correctly.