Pop top bolts

http://i1090.photobucket.com/albums/i372/stan999/Classics/1974 VW Baywindow Camper/Devon Roof Refurbishment/IMGP1349_zpsf9ac4332.jpg
Was planning on repainting and replacing with stainless, mine which have a little rust. I am struggling to undo them found the nut is 11mm what size is bolt head

 

The nuts and bolts are likely to be imperial, 7/16th head(11mm)
3/16ths UNF bolt and thread

 

Soak them in plus gas and rock them forwards and backwards whilst adding a little more plus gas
Use a ring spanner

 

Thanks all removed just need to source some new stainless ones with washers.