OOh! yours must be an update. Mine only says 45846
According to an ebay seller:
This is the #45846 darning plate that covers your feed dogs for free motion embroidery.
These are no longer made and hard to find!
Fits #45614 & 45718 needle plates.
And a Bonanza Seller I trust:
Sears Kenmore darning plate #45846 for Sears 158 machines with needle plates #45614 & 45718. Fitting models: 158.12110, 158.12111, 158.12112, 158.12120, 158.1212180, 158.13400, 158.17810, 158.1340281, 158.12121, 158.12311, 158.12312, 158.12312, 158.12313, 158.12411, 158.12412, 158.12510, 158.12511, 158.12512, 158.12520, 158.13410, 158.13413, 158.13450, 158.13500, 158.1350280, 158.1355080, 158.1561180, 158.1595281. and 158.17821 free arm and maybe others.