Old Nikon Buckmasters scope ring size

[Northmen]

I ordered 1 inch rings for my father's nikon buckmaster 3-9x40 scope. They seem to be to small for the scope. Every online search said 1 inch rings should fit. Before I order another set, do I get 30mm or was there a defect on the 1inch rings? Thank you in advance

 

[flyr]

Measure the tube with a caliper.
If the rings you got were the old style Leupold PRWs (or similar), the top ring half will have to be spread open a bit to go over the tube because the ring half goes beyond center on the tube.