534,611. Screwing die-heads. REIMSCHISSEL, C. A. May 30, 1939, No. 15855. [Class 83 (iii) ] A screwing die-head has the chaser holders moved radially into cutting position by a closing member, and a locking member co-operates with latch members which directly engage the locking and closing members to hold the chasers in cutting position, the locking member being adjustable on the body to predetermine the diameter of thread to be cut. In one form the head body 20 is attached to an adapter 21 on the machine spindle by means of a tapered plug 28, Fig. 2, which clamps the end of the body against a surface 31 of the adapter. Radial carriers 42, Fig. 2, provided with tangential chasers 50 adjusted by screws 56 and clamped by blocks 52, are moved by bevel closing ribs on tongues 106 carried by a sliding ring 110 which is normally pushed rearwardly by strong springs 115. The closing ring 110 is locked in the cutting position by radially slidable dogs 125 pressed outwards by springs 178 so as to engage an annular surface 164 of the ring, and the dogs are carried in radial dove-tailed grooves of a locking ring 130 which is adjustably screwed at 134 on the body 20 to vary the cutting size. A screw 137, Fig. 7, and soft pad 138 locks the ring 130 in adjusted position. In operation, the work is pushed into the die-head to start the threading operation and thereafter the chasers draw the work forward until the desired length of thread has been cut. A yoke (not shown) on the machine then slides a ring 150 rearwardly and causes a cam surface 171 thereon to push the dogs 125 inwardly until their surfaces 120 are clear of the surface 164 of the closing ring 110, thereby allowing the springs 115 to push this ring backwards and open the head. The head is re-set by means of the yoke, which pushes forward the rings 150 and 110 until the dogs 125 can be pushed outwards by their springs 178 to engage the end surface 164 of the ring 110. In a modified construction a central bush 220, Fig. 11, carrying an adjustable work-stop 223, is secured by a transverse pin 225 to the actuating ring 203, an axial slot being provided in the body to allow movement of the pin. The head is provided with taperthreading chasers and when the work engages the stop 223, which may be as soon as threading commences or after the first few threads have been cut, the ring 203 is pushed back to cam the dogs 210 inwards, these dogs being in this case carried by the closing ring 201. Inclined surfaces 241 slide along a similar surface on the locking ring 202 during the inward movement and allow the ring 201 to recede axially in order to produce a tapered thread, which may be longer than the width of the chasers. When the desired length of thread has been cut the dogs ride off the inner edge of the bevelled surface on the ring 202 and the springs may then slide the ring 201 rearwardly to open the head. The head is re-set as before, by a yoke pushing the rings 202, 201 forwardly. In this form, the pockets in the closing ring 201 which carry the axial opening springs are vented to prevent any cushioning or suction effect. Instead of separate springs 178, Fig. 2, or 235, Fig. 11, acting on the locking dogs, a single semi-circular spring may lie in an annular groove of the locking ring and engage the diametrically opposed dogs with its ends. Specifications 419,188 and 425,932 and U.S.A. Specification 1,456,805 are referred to. Cuttings, excluding from die-heads.-The forward portions of the actuating rings 150 or 203 co-act with a sleeve portion 160 of the head body in order to exclude chips, &c. Guiding chasers in die-heads.-The chaser carriers 42 are guided in rectangular section slots 62, Fig. 1 and 16, by T-shaped gibs 70 secured by screws 85 to the head body 20, removable shims being placed between the gibs and body and the gibs being flush with the forward face of the body. The carriers fit the slots are 60, 64 and 67 and the gibs at 92, but clearance is provided at 95 and 99.