TM 1-1500-204-23-2 (a) Theory of pipe thread seal.  The threaded portion of a pipe fitting Is tapered so that when it is tightened, the part with the external thread (male) Is forced into the internally threaded (female) part, creat- ing a seal. (b) Tightening fittings with pipe threads.  Ex- treme care shall be taken when tightening pipe fittings. Overtightening causes distortion, cracking, and leaks. Tighten 1/8-inch fittings to a torque of 125 to 175 Inch- pounds, 1/4-inch fittings of 200 to 300 inch-pounds, and 3/8-inch fittings to a torque of 300 to 400 Inch- pounds. (2) Tubing fitting thread lubricants.  Various lubricants and antiseize compounds are used on threads to prevent seizing and difficulty In disassembly. Threads that give the most trouble are male and female cast aluminum alloy tapered pipe threads Pipe threads secure their sealing features by interlocking of threads. Threads being tapered become highly stressed In final torqued condition Due to this high stress and peculiar stress-strain characteristics of aluminum alloy, threads may deform permanently, causing sufficient misalign- ment to make it difficult to disassemble unit.  It is highly desirable that male parts be made of different material and properly lubricated with antiseize compound. Federal Specification TT-S-1732, or equivalent Low pressure lines with low torque anodized aluminum alloy fittings and with antiseize compound used, may be disassembled under normal conditions. c .  Straight Pipe Thread.  Straight pipe thread is used on fittings In hydraulic components connected to tubing It Is shown in figure 4-26. d.  Universal Fittings AN 832.  AN 833.  and AN 834 Low Pressure.  These fittings are used for connecting tubing to components of the system and for connecting sections of tubing where the line passes through a bulkhead and fitting is secured to the bulkhead These fittings are satisfactory for pressures up to and including 1000 psi For Information pertaining to systems of over 1000 psi, refer to paragraph e Bulkhead fittings shall be installed on system components as follows: (1) Assemble nut on fitting end and screw all the way back to clear gasket groove. (2) Place gasket or equivalent performed pack- ing In gasket groove. (3) Screw fitting into boss until gasket contacts boss. (4) Unscrew fitting to approximate position desired but not more than 360 degrees (5) Tighten locknut lightly. (6) Assemble flared tubing to fitting. (7) Tighten locknut against boss e.  UniversalFittingsAN832.  AN833, andAN834 High Pressure. It is necessary to use a backup washer in the check nut when combination bulkhead and univer- sal fittings are installed In bosses on systems where pressures exceed 1000 psi This method eliminates the possibility of high pressure extending the rubber gasket into threaded areas of fitting.  A leather washer (MS28777) is used to prevent this extrusion of the rubber gasket A Teflon backup ring (MS9058) Is used in lieu of the leather washer in systems where tempera- ture in excess of 1600 F (710 C) are anticipated The method of installation is as follows: (1) Install nut as high up on fitting as possible. Add leather washer and gasket in position shown in detail A, figure 4-27. (2) Screw fitting assembly into boss until first thread at top of fitting groove is from 3/16- to 1/8-inch from top surface of boss, as shown In detail B, figure 4-27. (3) Hold fitting stationary and screw nut down until it seats on boss.  Slight extrusion of leather washer between surface of boss and nut is considered satisfac- tory, as shown in detail C, figure 4-27. (4) Tighten locknut against boss f.  Rosan Fluid Fittings.  The Rosan fluid fitting is a one-piece, thin wall insert with an external lockring The Rosan insert is fabricated from 6AL-4V titanium per AMS4967.  The lockring is fabricated from A-286 or- rosin-resistant steel per AMS5734 and is retained on the insert by a controlled interference fit.  The Rosan fluid fitting is used to provide semi-permanent port mounted installations and is compatible with Denature or flared tube ends.  The unique features of the Rosan fluid fitting are as follows. (1) Lockring provides positive lock. (2) No lacquering required. 4-20