Neither one, at least from what I can tell from the photographs.
The tray I currently have, though broken, is one-piece, U-shaped, and has four little rubber grommets fix-mounted in its sides, with studs poking out of said grommets to engage the holes in the drive.
It is SOMEWHAT similar in appearance to the 2LB09-01 caddy, as used in NetVista systems, although its rails are slimmer (in the vertical sense).
I believe it's the same caddy used in ThinkCentre M52's as well.
Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies
T61 14.1" SXGA+ and Windows 2000 Pro, soon to be XP (can't stand Vista), Atheros/IBM a/b/g Wireless card. Intellistations M Pro and Z Pro.
"Quid Malmborg in Plano" (Firesign Theater)