T5 or AT5? Timing Belt Tooth Profiles Compared With Real Dimensions
Industrial timing belts and matched pulley profiles
Target keyword: timing belt tooth profile comparison
Secondary: AT5 vs T5 timing belt, timing belt pitch chart, AT profile timing belt
Meta description: T and AT timing belt profiles share the same pitch but differ by up to 54% in tooth width. Full dimension tables from manufacturer data and why the profiles do not interchange.
T5 and AT5 both have 5 mm pitch. They will both fit around a pulley with 5 mm tooth spacing. They are not the same belt, and swapping one for the other will cost you either load capacity or positioning accuracy.
The difference is in the tooth, and it is bigger than most people expect.
T profile - the trapezoidal baseline
Standard T profile dimensions:
|
Profile |
Pitch t |
Overall height h |
Tooth height ht |
Tooth width s |
Flank angle |
|
T2.5 |
2.5 mm |
1.3 mm |
0.7 mm |
0.99 mm |
40° |
|
T5 |
5.0 mm |
2.2 mm |
1.2 mm |
1.78 mm |
40° |
|
T10 |
10.0 mm |
4.5 mm |
2.5 mm |
3.48 mm |
40° |
|
T20 |
20.0 mm |
8.0 mm |
5.0 mm |
6.51 mm |
40° |
Bottom tooth width: T2.5 = 1.50 mm, T5 = 2.65 mm, T10 = 5.30 mm, T20 = 10.15 mm.
The T profile is the metric trapezoidal standard - decades of installed base, widely stocked, inexpensive.
AT profile - advanced T
Standard AT profile dimensions:
|
Profile |
Pitch t |
Overall height h |
Tooth height ht |
Tooth width s |
Flank angle |
|
AT5 |
5.0 mm |
2.7 mm |
1.2 mm |
2.5 mm |
50° |
|
AT10 |
10.0 mm |
4.5 mm* |
2.5 mm |
5.0 mm |
50° |
|
AT20 |
20.0 mm |
8.0 mm |
5.0 mm |
10.0 mm |
50° |
\5.0 mm for ALPHA TORQUE and ALPHA POWER belts*
Bottom tooth width: AT5 = 3.62 mm, AT10 = 7.33 mm, AT20 = 14.66 mm.
The difference, quantified
|
Metric |
T5 |
AT5 |
Difference |
|
Pitch |
5.0 mm |
5.0 mm |
identical |
|
Tooth width |
1.78 mm |
2.5 mm |
+40.4% |
|
Bottom tooth width |
2.65 mm |
3.62 mm |
+36.6% |
|
Flank angle |
40° |
50° |
+10° |
|
Overall height |
2.2 mm |
2.7 mm |
+0.5 mm |
|
Metric |
T10 |
AT10 |
Difference |
|
Tooth width |
3.48 mm |
5.0 mm |
+43.7% |
|
Bottom tooth width |
5.30 mm |
7.33 mm |
+38.3% |
|
Metric |
T20 |
AT20 |
Difference |
|
Tooth width |
6.51 mm |
10.0 mm |
+53.6% |
|
Bottom tooth width |
10.15 mm |
14.66 mm |
+44.4% |
At 20 mm pitch the AT tooth is more than half again as wide as the T tooth. Same pitch, same tooth height, fundamentally different tooth.
Figure 1. Tooth width and root width, T against AT profile at identical pitch.
Why the wider tooth matters
The engineering rationale:
The AT belt has the widest teeth of all the trapezoidal profiles, and therefore the highest tooth shear resistance and the highest permissible specific tooth force. Low tooth deformation, strong cords and low backlash together give high positioning accuracy under load in linear drives."
Three linked effects from one geometric change.
Shear resistance. A belt tooth fails by shearing at its root. Shear capacity is proportional to the root cross-section, and AT's root is 36–44% wider.
Tooth deformation. A wide, stiff tooth deflects less under load. Deflection is lost motion - the pulley turns and the belt has not yet moved because the tooth is still compressing.
Positioning accuracy under load. This follows directly. On a linear axis, a T-profile belt deflects more per unit of force, so the position error varies with load. An AT belt with the same pitch holds position better, not because it is manufactured more precisely, but because its teeth are stiffer.
That last point is why AT dominates linear positioning. The advantage only appears under load - an unloaded comparison shows nothing.
The seating difference - and why they do not interchange
On how the AT tooth sits in the pulley:
AT10 profile timing pulley
Unlike the other trapezoidal profiles, the AT tooth rests on its head area in the tooth gaps of the pulley. The large tooth head also reduces wear and raises load capacity in conveyor drives, because surface pressure between the belt and the supporting rail is lower."
A T tooth and an AT tooth sit in the pulley groove differently. The AT tooth bears on its head area against the groove; the T tooth does not. The pulley groove profiles are correspondingly different.
Put an AT5 belt on a T5 pulley: the 2.5 mm tooth does not fit a groove cut for 1.78 mm, so it rides high, seats on its flanks, and the intended head contact never happens. Put a T5 belt on an AT5 pulley: the narrow tooth rattles in an oversized groove, giving backlash and impact loading at every engagement.
Same pitch is not the same belt. Match the profile to the pulley.
Double-sided and guided variants
DT profile (double-sided, Table 1.4.3) - for serpentine drives or where both belt faces drive:
HTD 5M profile timing pulley
|
Profile |
Pitch |
Overall height |
Tooth height |
Tooth width |
Flank angle |
|
DT5 |
5.0 mm |
3.4 mm |
1.2 mm |
1.78 mm |
40° |
|
DT10 |
10.0 mm |
7.0 mm |
2.5 mm |
3.48 mm |
40° |
|
DT20 |
20.0 mm |
13.0 mm |
5.0 mm |
6.51 mm |
40° |
Tooth dimensions match the single-sided T profile; only overall height increases.
TK profile (notched V-guide, Table 1.4.4) - for conveying where the belt must track laterally:
|
Profile |
Base |
Wedge width |
Wedge height |
Wedge angle |
|
T5K6 |
T5 |
6 mm |
4 mm |
38° |
|
T10K6 |
T10 |
6 mm |
4 mm |
38° |
|
T10K13 |
T10 |
13 mm |
6.5 mm |
38° |
The guide is notched rather than continuous, which allows a smaller minimum pulley diameter than a full-profile wedge. A continuous wedge resists bending; notching lets it flex around smaller pulleys.
Curvilinear and parabolic profiles
Beyond the trapezoidal families, rubber synchronous belts use curvilinear profiles (HTD, in 3M, 5M, 8M and 14M pitches) and modern parabolic profiles (in 2 mm, 3 mm, 5 mm, 8 mm and 14 mm pitches). The parabolic tooth form distributes stress more evenly through the tooth root than the semicircular HTD form, which is the basis for its higher power rating at the same pitch and width.
We are not going to quote a numeric parabolic-versus-HTD power advantage here. Those figures come from belt-manufacturer drive design manuals, and the product catalogues we work from are ordering documents rather than engineering manuals. If you need that comparison for a design decision, take it from the belt manufacturer's design manual rather than from any supplier blog - including ours.
What we can tell you is the pulley side: we cut HTD 3M, 5M, 8M and 14M, and the corresponding parabolic profiles, to the groove geometry the belt maker specifies.
Belt elongation
One figure worth knowing for linear axis design: permissible elongation for the AT5 profile in standard ST cord construction is ε_allowed = 0.47%.
On a 2-metre axis, 0.47% is 9.4 mm of permissible belt extension. That is why long belt-driven axes need either a closed-loop position measurement or a stiffer transmission element - belt elongation under varying load is a real position error, independent of tooth profile.
Choosing
T profile - general power transmission, conveying, light positioning, cost-sensitive, wide availability.
AT profile - linear positioning axes, higher torque at the same pitch, where tooth deflection under load matters, conveyor drives where surface pressure against a support rail is a wear concern.
DT - both faces need to drive.
TK / ATK - lateral guidance required.
FAQ
Can I fit an AT5 belt on a T5 pulley?
No. The AT tooth is 40% wider and seats differently. It will not sit in the groove correctly.
Is AT always better than T?
Better on load capacity and stiffness, more expensive and less widely stocked. For a lightly loaded conveyor, T is the sensible choice.
Why do T and AT have different flank angles?
40° for T, 50° for AT. The wider flank angle is part of how the AT profile gets its broader tooth root and its different seating behaviour.
What does the bottom tooth width tell me?
It is the root width, which governs shear strength. AT5 at 3.62 mm against T5 at 2.65 mm is the clearest single indicator of the capacity difference.
How much can a timing belt stretch?
Published permissible elongation for AT5 in standard ST cord is 0.47%. Over a long axis this is significant enough to require consideration in the control strategy.
Tianjin OuNaiDa Transmissions Technology manufactures timing belt pulleys in T, AT, HTD and inch profiles, in aluminium and steel, with taper bush or custom bore. Tell us the belt profile and width you are using and we will match the pulley groove profile correctly.
