Thread pitch converter

Good decisions start with honest arithmetic. No sign-up, no download, no data leaving your machine — just the calculation and a clear explanation.

The worked examples below use realistic figures, not textbook toys. Spend a moment on the quality of your inputs and the output takes care of itself.

What the calculator actually computes

The number pair encodes tensile strength (8.8 = 800 MPa tensile, 640 MPa yield). Thread pitch converter turns bolt, screw and nut specs into concrete numbers — torque, shear load, preload, weight. On technical fasteners errors are paid right away: too little torque means a loose joint; too much means stripped threads or a cracked head. For M10 8.8 that's about 47 Nm dry, ~35 Nm lubricated.

Check the head markings. Fasteners look simple but are critical on load-bearing assemblies.

Operating the calculator

Most widespread: using one torque figure for dry and lubricated joints (25% error). Third: over-tightening stainless — A2/A4 have 60–70% the strength of class 8.8 steel. Never increase torque to compensate for loosening — replace the fastener. Re-look over torque after 24 hours (preload drops 5–10% on first loading).

Second: ignoring property class — 4.6 and 12.9 need very different torque at the same diameter. For critical joints use a torque wrench with ±4% accuracy. For repeatedly disassembled joints — use self-locking nuts or spring washers.

Everyday scenarios

• Electrical supply: 230 V / 50 Hz, Types D, M and N plugs. Load-shedding still occasionally scheduled.
• Currency & format: South African rand (ZAR, R).
• VAT / sales tax: VAT is 15% on most goods and services. Basic foods (brown bread, rice, maize meal, dry beans, etc.) are zero-rated. Compulsory registration above R1 million turnover.
• Units of assess: Fully metric.
• Local notes: Amounts use rand, metric units and SARS defaults where applicable.

The arithmetic behind the result

Use before assembling a critical structure, when writing an engineering spec, when checking a torque-wrench installation, when computing weight for shipping, or when picking the right property class for the application. How this calculation applies in South Africa:

Lubrication cuts required torque 20–30% because less friction means the same torque delivers higher preload. Steel: 4.6, 5.6, 8.8, 10.9, 12.9. Example: a M10 class 8.8 bolt at friction coefficient 0.15 requires a specific torque in Nm.

Thread pitch converter turns standards into applied numbers so you don't rely on 'experience'.

When this page is worth a visit

DIN 933 (ISO 4017) — fully threaded. Only with designer approval.

Use 931 for shear joints, 933 for tension. 10.9 is 25% stronger tensile and used in preloaded joints (structural steel, engines).

DIN 931 (ISO 4014) — partial thread (plain shank under the head). Down-substitution risks shear failure or loosening.

Small habits, better numbers

South African costs move with tariffs and levies, so Thread pitch converter uses SARS-aligned rates and rand pricing. Recalculate after changing one input at a time; this shows which assumption controls the calculated outcome and makes an unexpected answer easier to diagnose. Every figure above applies to South Africa specifically and is reviewed when the rules change. For South Africa, use the units printed beside each field and do not assume that a familiar name means the same measurement system.

Frequent missteps

Start by checking the input fields rather than the final number. It builds on ISO 898 and DIN 933/931 plus the classic T = K × D × F calculation rule (T — torque in Nm, K — friction coefficient 0.15–0.20, D — nominal diameter in m, F — preload in N).

The values entered here are Metric size. Typical visitors are users in Johannesburg, Cape Town, Durban and Pretoria comparing offers or checking a bill, so the worked examples below use realistic local values rather than abstract numbers.

The bottom line

One computed figure hardly ever settles everything, but it normally settles where to begin. That is the whole trick: compute first, decide second.