TM 1-1500-204-23-2 a.  Flareless Fittings.  The main feature of MS fittings is that they can be used to connect unflared tubing.  An MS fitting has a counterbore in which the tube end is Installed.  In the half-sectional view of an MS fitting in figure 4-17, notice the 24-degree beveled portion of the counterbore and its seat.  The seat forms a slope for the tube during the connection of one tube to another tube or for a tube to a component and the beveled area causes the tube connector sleeve to seal the connection as the tube B-nut is tightened. (1) Identification of flareless fittings.  MS fit- tings are made of aluminum alloy or steel Aluminum alloy fittings can be identified visually by their yellow color, which is caused from the anodizing treatment. The cadmium plating on steel fittings are identified by letter-number codes; for example, MS21900-4, which is interpreted as follows: MS........prefix (military specification) 21900...design part number (adapter, flare- less tube to AN flared tube) 4..........size of fitting in sixteenths of an inch (4/16 (inch) The material from which the fittings are made is indi- cated by the absence of a letter at the end of the MS number or by the addition of a letter at the end of the number, for example: MS21900-4 is made from carbon steel MS21900-8-D is made from aluminum alloy MS21900-8-S is made from corrosion- resistant steel, class 347 (2)  Types of flareless fittings.  See figure 4-18 for examples of MS flareless fittings. WARNING Compressed air shall not be used for cleaning pur- poses  unless  reduced  to  less  than  30  psi  and  then only    with    effective    chip-guarding    and    personal protective equipment. (3) Installation of flareless fittings.  MS fittings must be inspected before Installation.  If It Is Impossible to see through a fitting or tube, blow clean, dry com- pressed air through it to be certain that no obstructions exist.  Any lines that have caps removed in storage or before installation should be flushed with clean hydraulic fluid.  Male threads and sleeves of the fittings being assembled should be lubricated with the type of hydraulic fluid used in the system On fittings with tapered threads, use antiseize compound on the threads, except for the first three, which are left dry. (a) Gasket. To make a connection be- tween tubing and a component, the proper gasket is selected, lubricated, and Installed In position as shown in figure 4-19.  The fitting is screwed into the boss of the component until it bottoms on the boss. (b) Installing tubing.  When connecting tubing to an MS fitting, the tube should be aligned with the fitting and the nut should be started by hand without excessive strain on the line (see figure 4-20).  Do not use force to align tubing Tube alignment can often be obtained by loosening clamps on connecting lines or by rotating fittings.  Both ends of the tubing should be connected and tightened until a decided increase In resistance to turning of the B-nut is encountered.  At this point, tighten the clamps, ensuring that they do not pull the tubing out of alignment and place it in a binding position.  Complete the installation by turning the B-nut one-sixth of a turn.  See figure 4-21 for turns and torque values.  Pressurize the hydraulic system and Inspect for leaks.  If leakage is noted, release system pressure and completely loosen the B-nut.  If possible, rotate the sleeve to a new position and then retorque the B-nut to its previous position plus one-sixth of a turn.  Normal- ly this will stop the leak, but If it does not, replace the assembly. 4-15