Thread Count (TPI) TPI stands for Threads Per Inch. This is simply a count of the number of threads per inch measured along the length of a fastener. TPI is used only with American fasteners. Metric Fasteners use a thread Pitch (see below). In general smaller fasteners have finer threads, so the thread count is higher.
Thread Pitch Metric fasteners are specified with a thread pitch instead of a thread count. The thread pitch is the distance between threads expressed in millimeters (measured along the length of the fastener). For example a thread pitch of 1.5 means that the distance between one thread and the next is 1.5mm. In general smaller fasteners have finer thread so they have lower thread pitch. Measuring Thread Count and Thread Pitch Thread count or pitch is normally measured using a Thread Gauge. US Threads Per Inch Table Threads Per Inch (TPI) Coarse Thread UNC Fine Thread UNF #2 56 - #3 48 - #4 40 - #5 40 - #6 32 - #8 32 - #10 24 32 #12 24 - 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 1-1/2 6 12 * 12tpi is the UNF standard however 14tpi is far more common in actual use. Metric Thread Pitch Table Table with 5 columns and 16 rows Bolt Diameter Thread Pitch Standard Fine Extra or Super Fine JIS 2 .4 - - .4 2.5 .45 - - .45 3 .5 - - .5 4 .7 - - .7 5 .8 - - .8 6 1.0 - - 1.0 7 1.0 - - 1.0 8 1.25 1 - 1.0 10 1.5 1.25 1 1.25 12 1.75 1.5 1.25 1.25 14 2 1.5 - 1.5 16 2 - - 1.5 18 2.5 - - 1.5 20 2.5 - - 1.5 ********************************************************************** This message and its attachments may contain legally privileged or confidential information. If you are not the intended recipient, you must not disclose or use the information contained in it. If you have received this e-mail in error, please notify the sender immediately by return e-mail and delete the e-mail. Any content of this message and its attachments which does not relate to the official business of Eraring Energy must be taken not to have been sent or endorsed by Eraring Energy. No warranty is made that the e-mail or attachment(s) are free from computer virus or other defect. ********************************************************************** [Non-text portions of this message have been removed]
