The M1-S and M1-D models are based on 3,5" disk drives.
=== FM1 (3,5" + 5,25") ===
Later on, Vortex also offered a bundle consisting of a single 5,25" drive (F1-S) and a single 3,5" drive (M1-S). Remarkably, Vortex used the X-Drive housings for this special offer.
=== FDA-1 3" Drive Adapter ===