Trapezial thread

Not used in screws and bolts, trapezoidal threads are used to make actuating or force-transmitting screws, with one or more threads. They accept heat treatments better than triangular nets.

Spiral pitch Ph: corresponds to the axial displacement per revolution of the screw.

Pitch of the profile P: it is equal to the axial distance between two consecutive homologous sides.

Examples:

for a screw with 1 thread Ph = P; for a screw with 2 threads Ph = 2P; for a screw with n thread Ph = nP.

Noticed :

the NF ISO 2901 standard offers two profile options:

• profiles with hollow on the underside of the thread and without play on the flanks (allowing better centering between screw and nut or better concentricity); profiles with opening at the bottom of the thread and with clearance at the sides (for more general use).

Indication :

For left-hand threads, add the letters LH to the end of the designation.

Screwing or tapping with 1 thread: letter Tr.

the nominal diameter (in mm); the sign X; the pitch (in mm); A dash; the sidewall tolerance number and deviation letter.

Examples:

Tr 40 x 7 - 7th (screw with 1 right-hand thread nominal diameter 40 mm and pitch P = 7 mm; in 7th quality).

Screws or taps with multiple threads: letter Tr, the nominal diameter (in mm); the sign X; the screw pitch (in mm); in brackets the letter P followed by the value of the pitch of the profile P; A dash; wire quality.

Examples:

Tr40 x 14 (P7) LH - 8H, for taps with 2 left-hand threads with nominal diameter 40 mm, pitch P = 7 mm, bevel pitch Ph = 14 mm and quality 8H.