Apologies for the probably daft question, I am thinking of buying a small KURODA ball screw (180 mm overall length, 8mm diameter, 2mm lead). I have a photo from the seller and I noticed a wider area towards one end of the screw. I suspect it is for mounting a pulley (it seems to have a screw flat area). Can you please confirm if my understanding is correct?
That is a wrench flat, presumably used when installing a nut on the conventional threaded portion at the left end.
The overall enlargement into which the wrench flat is machined probably faces either a bearing or possibly some short of pulley that would installed between it and the threaded portion to the left.
It could be used for a sprocket/gear/pulley but that is not its purpose.
The driven end of the screw is usually attached directly to a motor shaft by a flexible collar which allows some minor misalignment. The part marked "End support mount" has a threaded portion for the nut to lock the shaft into the end bearing.
The undriven end is allowed to "float" in its bearing to allow for expansion, usually secured with a circlip.
The part with the flat is then on the inside of the bearing and inside the machine. It is not a required part of the mechanism and appears unique to that manufacturer.