this came from an American flat track bike. gearing needed raising so they fitted a larger 60 tooth sprocket.

presumably they found a spare alloy sprocket and bored to fit, as it sits on top of the original teeth, alignment stays as made

solved a problem. may need more bolts for security.

also including original front sprocket 19 tooth 40-3123

may be useable if you want something different, please see pictures as part of description.