Some kinds of taper keys have screwed ends, for the convenience of having a nut to prevent the key slipping back from its place while in use. The longitudinal axis of the portion intended for the screw is sometimes in the same line with the longitudinal axis of the taper part of the key; it is always necessary for the smith to know the required position, that he may not leave a larger quantity of iron for turning than is sufficient when the part to be screwed is in its proper position.

After the extremity is carefully welded and curved, the reducing to form the stem is commenced by top and bottom fullers. These are driven in at the spot intended to be the termination of the taper portion, and the commencement of the screw part. This screw part or stem is first made eight-sided by reducing with the hammer, and then rounded by means of angular gap tools, which thoroughly close together the fibres of the iron; if this is not done, a good screw cannot be produced on the key-stem. If the extremity of this stem is hollow or concave, instead of being properly curved, there is a liability of the stem becoming split in some part, although the outside may appear solid. The split could be remedied by welding, but in some cases the stem would then be too small. One kind of split-stem is shown by Fig. 83.