It's a 3/8"-16 coarse thread flanged hex bolt, 3 1/4", blue loctite, it goes into the bottom of the oil pan through a deep hole, perpendicular to the crankshaft. Microcat or rovers north do not list the part in their diagrams. There are two of them.

 

This item is not unique to Rovers. You have the specs; find the bolt somewhere (anywhere) else. Lowe's? Home Depot? What's wrong with the ones you removed? Add your own Loctite.