This is a 40 tooth sprocket with what appears to be a 1-1/2" bore but without an actual measurement I can't be sure. The first part of the part number on the sprocket (40B) is the chain size or a #40 chain. The second part of the part number is the tooth count (40HF) The 104 is probably the manufacture's catalog designation. This is basically a generic sprocket that could be used for many different applications. The one shown in the URL supplied is for a #40 chain (40B) and has a 3/4" bore and 45 teeth (45H) but is of the same design. Yours could be made by the same manufacturer but there are lots of different makers. It is impossible to know the exact application of this sprocket.

This is a 40 tooth sprocket with what appears to be a 1-1/2" bore but without an actual measurement I can't be sure. The first part of the part number on the sprocket (40B) is the chain size or a #40 chain. The second part of the part number is the tooth count (40HF) The 104 is probably the manufacture's catalog designation. This is basically a generic sprocket that could be used for many different applications. The one shown in the URL supplied is for a #40 chain (40B) and has a 3/4" bore and 45 teeth (45H) but is of the same design. Yours could be made by the same manufacturer but there are lots of different makers. It is impossible to know the exact application of this sprocket.

References:

https://www.ebay.com/itm/Finished-Bore-Sprocket-40B45H-3-4-Bore-Sprocket-New-...