Rivet question

[bronsonarlo]

What type/size rivet is used to attach the main roof to the galvanized roof/rain gutter. The top of the rivet has a donut shaped head. Thanks

[Dav1550]

Truss head , Semi-tubular aluminum …….
3/16 dia. X 5/16 L ……are near exact replacement.
3/16 dia. X 3/8 L …… Is what I ended up using, as I was a bit more generous with the sealer and after re- galvanizing the gutter was a shade thicker.