For the sake of completeness, the three additional belt profiles shown in Figure 19j, 19k and
19l are used in Europe and are sometimes found on machinery imported from Europe and Japan.
They are not produced in the U.S.A. and are not covered by RMA standards. The belts are made
of polyurethane, and steel is usually used as the tension member.
As described in previous sections, the presently known most advantageous belt tooth
configuration is the Gates PowerGrip
GT2. This is a result of continuous improvement of the
previous HTD tooth profile. The HTD profile is protected by U.S. Patent Number 4,337,056,
whereas the GT2 profile is described in U.S. Patent Number 4,515,577.
Pulleys for these belt profiles are usually available from manufacturers licensed by
Gates Rubber Company. Stock Drive Products is one of the companies who can supply a
full range of these pulleys as standards or specials, per customers' drawings.
SECTION 8 PULLEY PITCH AND OUTSIDE DIAMETERS
Pulley and belt geometry as indicated in Figure 1 shows reference to a Pitch Circle, which is larger
than the pulley itself. Its size is determined by the relationship:
where P is the belt tooth spacing (pitch) and N is the number of teeth on the pulley. The reinforcing
cord centerline will coincide with the pulley pitch diameter while the belt is in contact with the pulley. At
the same time, the outside diameter of the pulley will be in contact with the bottom of the belt tooth.
Hence, the distance U between the reinforcing cord centerline and the bottom of the belt tooth will
determine the outside diameters of pulleys for different pitches. See Table 4.
Distance from Pitch Line
to Belt Tooth Bottom U
O.D. = pd 2U
3 mm HTD
5 mm HTD
8 mm HTD
2 mm GT2
3 mm GT2
5 mm GT2
T2.5 (2.5 mm)
T5 (5 mm)
T10 (10 mm)
Due to the particular geometry of the 8 mm HTD belts, some corrections are needed for small-size
pulleys only. Hence, consult pulley specifications tables given later in this text, pertaining to the 8 mm
As previously noted, the pitch and the number of teeth will determine the pitch diameter of the
pulley, whereas its outside diameter will depend on the U dimension (distance from tooth bottom to
centerline of cord) as shown in Table 4.
Table 4 Basic Belt Dimensions