How to Measure a Screw
Length, diameter (gauge), and thread pitch — a step-by-step walkthrough using calipers, a thread gauge, or plain household tools.
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Technical, measurement-first guides for identifying, measuring, and specifying screws and bolts. No fluff. Just the numbers and the diagrams you need.
How to Measure a Bolt
Under-head length, major diameter, thread pitch, and grade markings — the four measurements that fully identify any bolt.
Read guideScrew Size Identifier
Pillar reference covering every common screw designation, gauge-to-millimeter conversions, and when each system is used.
Read guideBolt Size Identifier
Hex, socket cap, carriage, and flange bolts — how to read the designation and confirm it with a caliper and thread gauge.
Read guideMetric vs SAE Bolt Conversion
Side-by-side charts for M-series and fractional bolts. Which sizes are close cousins, which ones will cross-thread, and how to tell.
Read guideM6 vs 1/4-20: Are They Interchangeable?
They look identical but they're not. Exact diameter and thread pitch differences, what happens when you force them, and how to tell them apart fast.
Read guideGrade 5 vs Grade 8 Bolts: Strength & Markings
3 head lines vs 6 head lines. 120,000 vs 150,000 psi. Know which grade to use — and when substituting down is dangerous.
Read guideTypes of Screw Heads & Drives: Phillips, Torx, Hex & More
Complete visual reference for flat, pan, hex, and socket cap heads — plus Phillips, Torx, Robertson, Pozidriv, and Allen drives. Diagrams and application guide included.
Read guideThread Pitch Chart: TPI to Metric Conversion (Printable)
Full metric pitch chart (M1.6–M36 coarse and fine) plus TPI-to-mm conversion for UNC/UNF threads. Includes how to measure thread pitch without a gauge and near-match lookalikes to avoid.
Read guideHow to Remove a Stripped Bolt: 7 Methods That Actually Work
Rubber band to drill-out — 7 methods ordered from least invasive to last resort. Covers extractor sockets, left-handed drill bits, penetrating oil, and when to re-thread the hole.
Read guideM8 vs 5/16 Bolt: Why You Can't Substitute (And What To Use Instead)
M8 and 5/16" share a near-identical diameter (8.00 mm vs 7.94 mm) but incompatible thread pitches — forcing one into the other strips threads. Includes side-by-side specs, how to tell them apart without a gauge, and safe substitution options.
Read guideDrywall Screw Size Guide
Coarse vs fine thread, bugle head explained, length chart for 1/2" and 5/8" drywall, and ceiling vs wall rules. Covers W-type, S-type, and double-layer assemblies.
Read guideDeck Screw Size Chart: Length, Gauge & Material Guide
#8 × 3" for 5/4 decking, #10 × 3-1/2" for 2× lumber. Covers material selection (stainless vs HDG for PT lumber), drive types, composite deck requirements, and structural fastener rules.
Read guidePhillips vs Torx Screws: Why Pros Switched and When to Use Each
Torx eliminates cam-out; Phillips provides controlled depth stop. Covers drive size cross-reference (T20/T25 vs #2/#3), which applications need which, bit kit recommendations, and Pozidriv warnings.
Read guideHow to Identify a Screw Without Calipers (5 DIY Methods)
No calipers? Use the on-screen ruler, a steel ruler + thread count, coin comparison, or the hardware store bolt board to identify any screw in under 90 seconds. Includes a common size reference chart.
Read guideLag Bolt Size Chart: Diameter, Length & Pilot Hole Guide
Lag bolt size chart for every common application: deck ledger 1/2" × 4", fence posts 3/8" × 3–4". Includes the two-step pilot hole method, IRC code requirements for ledger boards, and when to use structural screws instead.
Read guideMachine Screw vs Wood Screw: Differences and When to Use Each
Blunt tip = machine screw; sharp point = wood screw. Covers the three visual tells, full spec comparison, how to find the right replacement, and why you can never swap one type for the other.
Read guideSelf-Tapping vs Self-Drilling Screws: Which Do You Need?
Self-tapping screws need a pilot hole; self-drilling (Tek) screws drill their own entry with a fluted tip. Includes a Tek point rating chart (Tek 1–5), pilot hole sizes for #6–#12 gauges, and a quick decision guide for HVAC, appliance, and auto repair jobs.
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