What it is and where it fits
The Telemecanique XS612B1PAL10EX is a tubular inductive proximity sensor — the cylindrical, M12-style form factor that bolts into a standard bracket or through a panel hole. It's listed under sub-category 'Tubular Inductive Proximity Sensor', so you're getting the round-body sensor common on packaging machines, conveyors, and pick-and-place stations where space is tight and the target is ferrous.
Why a rectangular sibling won't drop in
The XS612B1PAL10EX is a tubular inductive proximity sensor; the XS8D1A1MAL10 is a block/rectangular type. Their mounting geometries differ — tubular uses a round bracket or clamp, rectangular uses a flat surface and corresponding cutout.