The front and rear gas-check cups are of steel, and hold between them a plastic pad made of certain proportions of asbestos and tallow and covered with canvas (with disks of copper (_m_) on either side in the revised model,) and a diagonally-split ring (_n_) of steel is used to cut off the escape of gas. A spiral spring (_j_) surrounds the stem of the obturator at the rear of the block, and bears against a shoulder on the block and a nut (_h_) on the screw-thread of the spindle. This spring, which acts to press the spindle back, keeps the cups and pad in place, takes up any set of the pad due to firing, and prevents the fracture of the screwed end of the stem. The spline-screw (_k_) holds the nut on the spindle in position and prevents its unscrewing when the pad sticks in its seat after firing. [Illustration:THE FREYRE OBTURATOR. FIG. 35.] The principal parts are (Fig. 35): the spindle (_a_); the gas-check ring (_f_); the spring (_e_); the obturator-nut (_d_); the locking-nut (_d′_), or the spline-screw. The =Spindle= has a head (_g_) at the forward end, its surface being plane and its sides conical, with the larger diameter of the cone in front. The vent (_c_), 0.2 inch in diameter, passes through the axis of the spindle, and the copper bushing (c) is inserted by pressure at the front end. The =Gas-check Ring= (_f_) is nearly triangular in section, coming to a point at the front. It fits accurately on the conical surface of the head of the spindle, and is slightly longer in the direction of the axis of the bore than this head. Its rear surface rests against the front surface of the block, while the rear surface of the head is not in contact with this front surface, and can only be brought in contact with it by a heavy pressure, which will expand the gas-check ring. The =Spring= (_e_) acts against a shoulder in the block and a corresponding shoulder on the obturator-spindle, and tends to press the spindle forward. =The Obturator-nut= (_d_) prevents the action of the spring from forcing the spindle too far forward, and also regulates the tension of the spring. The spline-screw acts as in the de Bange system. This screw is used in place of the locking-nut (_d′_) shown in figure. THE LEVER-HANDLE. (See Fig. 37.) This handle (_h_) acts as a lever to rotate the block, its head acting as a cam to withdraw the block and obturator when the latter sticks after firing, and to lock the block in the carrier-ring and prevent rotation during firing. It is supported in the lugs (_l_) of the breech-block by a pin (_e_) and rotates with the pin; to which it is secured by a screw entering vertically. The head of this pin has a projection (_a_) which strikes against the corresponding stop on the right lug and limits the motion of the lever-handle. THE BRONZE-HANDLE. (See Fig. 37.)