Picture of How to fit a saddle stop to a lathe
Maurice Rhodes talks http://www.model-engineer.co.uk/ through fitting a saddle stop.

There are two disadvantages to this positioning of the stop-rod. The first is the liability of swarf to fall between the saddle and rod, but this is no real problem since this will produce a shorter lengthwise cut. The swarf is then brushed away prior to the final finishing cut

For repetitive work and rough turning a workpiece mounted in the chuck, a saddle-stop fitted to the lathe can save the worry of overshooting the length of a cut and so allow for more concentration on the diameter of the work. After the workpiece has been faced-off, it's so easy to adjust the length of the cut more accurately if a drill bit, feeler gauge or whatever, is slipped between the saddle and the stop-rod of the attachment rather than trying to make the measurement in other ways. Taking lengthwise measurements on the small lathes such as the Unimat 3 can be a little difficult at times, within the restricted area available.

The first simple saddle-stop, Fig.1, photo 1 & photo 2 was the first to be fitted to my own machine and was used successfully for quite some time. However the time came when thread cutting in the lathe was to be carried out and the Unimat threading accessory could not be fitted, due to the obstruction of the saddle-stop clamp-bracket.

Second is the need to cut a clearance for the stop rod in the clamping plate of one of the supports of the threading attachment and also that of the fixed-steady if these are part of the owner's kit. Alternatively it may be possible to reposition the saddle stop bracket to allow the stop rod to pass between the clamp plates and the relative accessory, but the easy option is to remove the stop-rod whenever these items are to be used.