Mandrels, used for turning the full length of an OD. They would be very slightly tapered, with the nominal diameter that is stamped on them roughly at their midpoint. The small end should be the same relative to the stamped writing (or incised groove) for each of them (i.e. the stamping will either tell you the big end or the small end not a random mixture of both possiblities). You would use them between centres, with the cutting force pushing the part towards the big end. I think they can also be called arbors, hence an arbor press is used to push them onto the stock or to remove them when finished.
The first pic are parallel workholding arbors for a union tool and cutter grinder. I know because the lady I bought my grinder off unwittingly sold them in another lot which I bid on to get the arbors but got sniped. You can see them in use in the pic below.
The 2-piece ones in the second pic look like expanding parallel arbors.
If you're selling them I would pay £30 for the lot.