Threaded Hole Engagement & Torque

1 · Thread

Thread system

Series filter

Size

Class (ext / int)

Override thread limit dimensions (nonstandard / oversize-tapped / plated threads)

Basic major dia, D

Threads per inch, n

1/in

Min major dia, ext (D_{s min})

Min pitch dia, ext (E_{s min})

Max minor dia, int (K_{n max})

Max pitch dia, int (E_{n max})

2 · Materials

External (bolt/stud)

Tensile ultimate, F_tu ext

Tensile yield, F_ty ext

Shear ratio F_su/F_tu, ext

—

Internal (tapped material)

Tensile ultimate, F_tu int

Shear ratio F_su/F_tu, int

—

Preset strengths are typical spec minimums — verify against the project material spec / MTRs. Shear ratio ≈ 0.60 steel, 0.55 austenitic SS, 0.55–0.65 aluminum, ~1.0 gray iron. FED-STD-H28 & the MH L_e formula implicitly assume F_su = 0.5·F_tu.

3 · Design basis

Develop full bolt strength — bolt breaks before threads strip (A_t·F_{tu ext})

Carry a specified tension load with a safety factor

Applied tension load, P

SF on thread strip

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SF guidance — applied to ultimate thread-strip capacity. 2.0: typical for preloaded machinery / structural joints in ductile, well-characterized material (basis of the legacy Rev 1 sheet). 3.0–5.0: lifting & rigging, pressure boundaries, castings, or uncertain tapped-material properties. 1.25–1.5: only where the applied load is already a factored / ultimate load. This SF does not cover fatigue, vibration loosening, or thermal effects; torque–preload scatter is handled separately in section 5.

4 · Tapped hole geometry

Hole type

Specified full-thread depth, d_t

Entry chamfer / countersink

pitches

Bolt-point / bottom deduction

pitches

Deductions convert nominal thread depth to effective engagement: entry countersink, plus incomplete point threads on the bolt end in a blind hole (~2P). If the bolt point extends past a through hole, set the bottom deduction to 0.

Boss OD / edge distance ×2 (opt.)

5 · Preload & torque

Max allowable preload (lesser of thread strip / SF and bolt yield basis)

Specified target preload

Target preload, F_p

Bolt preload limit, fraction of F_ty

—

Nut factor, K

K value

—

Torque–preload scatter, ±

Results — required depth & torque

Required full-thread depth

—

Installation torque

—

Specified depth check

—

Threaded Hole Engagement & Torque

1 · Thread

2 · Materials

3 · Design basis

4 · Tapped hole geometry

5 · Preload & torque

Results — required depth & torque

Thread profile — engaged (schematic, radial dims not to scale)

Thread geometry & areas

Engagement length

Capacities at specified depth

Preload & torque detail

Calculation summary (substituted formulas)