Thread Count (TPI) Explained
- TPI stands for Threads
Per Inch which is simply a count of the
number of threads per inch measured along
the length of a fastener. This description
is used only with American fasteners.
Metric Fasteners use a thread Pitch to
designate different thread sizes.
|
Bolt
Size
No. or Inches
|
Threads
Per Inch (TPI)
|
|
Coarse
Thread
UNC
|
Fine
Thread
UNF
|
|
#0
|
-
|
80
|
|
#1
|
64
|
72
|
|
#2
|
56
|
64
|
|
#3
|
48
|
56
|
|
#4
|
40
|
48
|
|
#5
|
40
|
44
|
|
#6
|
32
|
40
|
|
#8
|
32
|
36
|
|
#10
|
24
|
32
|
|
#12
|
24
|
28
|
|
1/4
|
20
|
28
|
|
5/16
|
18
|
24
|
|
3/8
|
16
|
24
|
|
7/16
|
14
|
20
|
|
1/2
|
13
|
20
|
|
9/16
|
12
|
18
|
|
5/8
|
11
|
18
|
|
3/4
|
10
|
16
|
|
7/8
|
9
|
14
|
|
1
|
8
|
12
|
|
1-1/8
|
7
|
12
|
|
1-1/4
|
7
|
12
|
|
1-3/8
|
6
|
12
|
|
1-1/2
|
6
|
12
|
| 1-3/4 |
5 |
|
| 2 |
4-1/2 |
|
| 2-1/4 |
4-1/2 |
|
| 2-1/2 |
4 |
|
| 2-3/4 |
4 |
|
| 3 |
4 |
|
| 3-1/4 |
4 |
|
| 3-1/2 |
4 |
|
| 3-3/4 |
4 |
|
| 4 |
4 |
|
