Pipe threads are always specified as National Pipe Thread . NC, NF (etc) refer to bolts. Pipes are measured by their i.d. BTW so the pipe that would fit in place of the plug should have a 1/2" id. The pipe plug that they're referring to should have a 1/2" square hole in it. A 1/2" racket handle should fit right in.
I hate that oil spill on the skid plate, when draining - any ideas?
Look at Vernco.com. He has a LOT of good ideas about how to deal with things like this. Also see <http://www.vernco.com/Tips/id321.htm>
Joined: Apr 22, 2012 Posts: 119 Location: the Netherlands
Posted: Mon Apr 29, 2013 3:18 am Post subject:
Hi Philip,
More information about your question:
All the plugs are the same for the Transmission/Transfer filling and drain plug.
The Plug Mfr# Wo-801660, thread size NPTF 1/2" TPI 14,major dia .8351".
NPTF=American Taper Pipe Thread for Dryseal joint without sealent compound.
Chris _________________ 2x 1956 M38A1(Nekaf);1954 1/4TON trailer,Polynorm(Dutch);1983 Honda VF750C (Magna)
Sometimes NPT threads are referred to as MPT ('Male Pipe Thread'), MNPT, or NPT(M) for male (external) threads; and FPT ('Female Pipe Thread'), FNPT. An equivalent designation is MIP (Male iron pipe) and FIP (Female iron pipe). Also the terms NPS and NPSM are sometimes used to designate a straight, not tapered, thread. This should not be confused with NPS, meaning Nominal Pipe Size.[citation needed]
NPTF is pipe thread "fuel" often used in hydraulics. A taper is cut on the id of male pipe to accommodate metal to metal seals using swivels. NPSH is straight thread using the same pitch, thus NPSH female fittings are often used on NPT male fittings to have hand tight gasket sealed fittings to adapt to other thread types. A good example is adapting to NST for fire service.[citation needed]
Sometimes these terms are used:[citation needed]
MIP: stands for Male Iron Pipe, or Male International Pipe, or MPT Male Pipe Thread. It is a term for pipe fittings.[citation needed]
FIP: stands for Female Iron Pipe, or Female International Pipe, or FPT. It is a term for pipe fittings that MIP fittings fit into.[citation needed]
The difference between FIP, MIP, and Compression fittings is in the tapering of the thread. FIP has taper of 1:16 (6.25% slope), compression has taper of 13:96 (13.5% slope).[citation needed]
A female iron connection has a tapered thread, which thins out to the end of the pipe. As the fitting is tightened, the ever-decreasing thread depth means that the connection becomes watertight. To properly seal the fitting, paste thread sealant or PTFE (polytetrafluoroethylene) tape more commonly called Teflon tape, wrapped around the thread is required.[citation needed]
MIP fittings are usually found in thicker copper pipe, iron pipe, steel pipe, gas pipe, gas stove, gas oven, gas heater, and gas water heater connections.[citation needed]
[edit]Specifications
The taper rate for all NPT threads is 1⁄16 per inch (3⁄4 inch per foot) measured by the change of diameter (of the pipe thread) over distance. The angle between the taper and the center axis of the pipe is 1° 47′ 24″ (1.7899°). Commonly-used sizes are 1⁄8, 1⁄4, 3⁄8, 1⁄2, 3⁄4, 1, 1 1⁄4, 1 1⁄2, and 2 inch, appearing on pipes and fittings by most U.S. suppliers. Sizes smaller than 1⁄8 inch are occasionally used for compressed air, while sizes larger than 2 inches are uncommon, due to the use of alternative methods of joining that are used with these larger sizes. NPT is defined by ANSI/ASME standard B1.20.1.[1]
Nominal Pipe Size is loosely related to the inside diameter of Schedule 40 pipe. Because of the pipe wall thickness, the actual diameter of the threads is larger than the NPS, considerably so for small NPS. Other schedules of pipe have different wall thickness but the OD (outer diameter) and thread profile remain the same, so the inside diameter of the pipe is therefore different from the nominal diameter.[citation needed]
Threaded pipes can provide an effective seal for pipes transporting liquids, gases, steam, and hydraulic fluid. These threads are now used in materials other than steel and brass, including PTFE,[2] PVC, nylon, bronze, and cast iron.[citation needed]
The taper on NPT threads allows them to form a seal when torqued as the flanks of the threads compress against each other, as opposed to parallel/straight thread fittings or compression fittings in which the threads merely hold the pieces together and do not provide the seal. As the thread body is tapered (0.75 in/ft) a larger diameter keeps compressing into a smaller diameter and finally forms a seal (no clearance remains between the crests and roots of the threads because of the taper). This means that NPT fittings should be burr free and lubricated using a lubricating material like lubricating paste or tape. The use of tape also helps to limit corrosion on the threads, which otherwise can make future disassembly nearly impossible.[citation needed]
A semi-compatible variant called National Pipe Taper Fuel (NPTF), also called Dryseal American National Standard Taper Pipe Thread, defined by ANSI B1.20.3, is designed to provide a more leak-free seal without the use of teflon tape or other sealant compound. NPTF threads are the same basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leakage path.[citation needed]
Nominal pipe size (in) Pipe outer diameter Threads per inch Thread pitch
1⁄16 0.3125 in (7.94 mm) 27 0.03704 in (0.94082 mm)
1⁄8 0.405 in (10.29 mm) 27 0.03704 in (0.94082 mm)
1⁄4 0.540 in (13.72 mm) 18 0.05556 in (1.41122 mm)
3⁄8 0.675 in (17.15 mm) 18 0.05556 in (1.41122 mm)
1⁄2 0.840 in (21.34 mm) 14 0.07143 in (1.81432 mm)
3⁄4 1.050 in (26.67 mm) 14 0.07143 in (1.81432 mm)
1 1.315 in (33.40 mm) 11 1⁄2 0.08696 in (2.20878 mm)
1 1⁄4 1.660 in (42.16 mm) 11 1⁄2 0.08696 in (2.20878 mm)
1 1⁄2 1.900 in (48.26 mm) 11 1⁄2 0.08696 in (2.20878 mm)
2 2.375 in (60.33 mm) 11 1⁄2 0.08696 in (2.20878 mm)
2 1⁄2 2.875 in (73.03 mm) 8 0.12500 in (3.17500 mm)
3 3.500 in (88.90 mm) 8 0.12500 in (3.17500 mm)
3 1⁄2 4.000 in (101.60 mm) 8 0.12500 in (3.17500 mm)
4 4.500 in (114.30 mm) 8 0.12500 in (3.17500 mm)
5 5.563 in (141.30 mm) 8 0.12500 in (3.17500 mm)
6 6.625 in (168.28 mm) 8 0.12500 in (3.17500 mm)
8 8.625 in (219.08 mm) 8 0.12500 in (3.17500 mm)
10 10.750 in (273.05 mm) 8 0.12500 in (3.17500 mm)
12 12.750 in (323.85 mm) 8 0.12500 in (3.17500 mm)
14 14.000 in (355.60 mm) 8 0.12500 in (3.17500 mm)
16 16.000 in (406.40 mm) 8 0.12500 in (3.17500 mm)
18 18.000 in (457.20 mm) 8 0.12500 in (3.17500 mm)
20 20.000 in (508.00 mm) 8 0.12500 in (3.17500 mm)
24 24.000 in (609.60 mm) 8 0.12500 in (3.17500 mm)
And from the CTS tool site:
Quote:
NPT Vs. NPTF Taper Pipe Threads
The two most common taper pipe threads used in the United States are NPT and NPTF. Applications range from electrical conduits and hand railings to high-pressure pipe lines that carry gas or caustic fluids. NPT threads are for mechanical or low-pressure air or fluid applications and require the use of sealing compounds like Teflon tape, to provide the seal. When the application is more critical, and the sealing compound may fail due to high heat or pressure, NPTF Dryseal threads are used. This mechanical seal is produced by the mating and slight crushing of the threads when a wrench is applied to tighten the fittings.
Visually, both threads appear to be identical. Both have a ¾” taper over one foot of length. Both have the same pitch diameter at the top of the hole of internal threads or end of the pipe on external threads, and both have the same thread lengths or depths. However, there is a subtle difference in the thread form that differentiates the two. The major and minor diameters of both threads differ slightly. With NPT threads, after a wrench is applied, slight spaces at the major and minor diameters may exist that would allow the assembly to leak and therefore a sealing compound is used to fill any gaps. On the other hand, NPTF threads are designed to ensure that sufficient crushing of the entire thread form will take place to produce a mechanical seal.
How does the difference in thread forms effect the tooling used to produce NPT and NPTF threads? Taps are available for both NPT and NPTF threads having the appropriate form to produce each type of thread. Since NPT threaded parts require sealing compounds, it is acceptable to use an NPTF tap for NPT applications. However, NPT taps cannot be used for NPTF applications, as it will likely produce a thread that will leak. The same is true of external threads. In most cases the tap drill is the same for both forms.
The most significant difference in the two threads is the inspection required. Since sealing compounds will be used for NPT threads, only a single plug with a step, known as an L1 plug (internal thread) or a single thin L1 ring (external) are required to check size. However, since the taper and the position of major and minor diameters are so critical to the sealing of NPTF threads, the additional threads in the assembly known as L2 and L3, and the major and minor diameters are inspected with either special plug or ring gages.
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