The F.A.S.T. 401 SD is a yo-yo produced by YoYoFactory as part of the F.A.S.T. 400 series. It was first released on December 26th, 2008.
Description[]
The F.A.S.T. 401 SD is similar in design to the older F.A.S.T. 401k, but is about 2mm narrower, along with the outer edges being thickened a little to form a slight H-shaped profile.
Nevertheless, it features the F.A.S.T. 400 Series shuttles and adjustment knobs. There are ninety response settings on each body half of the yo-yo, and the shuttles can be interchanged with response pads, so that the user could use only pads, only shuttles, or a hybrid of both. The 401 SD also uses an A-sized Dorothy bearing, which was replaced with a SPEC bearing later on in the yo-yo's retail lifespan.
Along with the later Adjust-O-Matic, the 401 SD is one of the very last yo-yos made as part of the F.A.S.T. 400 Series.