Thanks for the offer @
towcat ! That was really helpful and actually jogged my memory. Found them this morning. I forgot they were flanged. I have a hardware order to put in this week anyway so I'll pick up some new ones. Need other random nuts, bolts etc. Once I get a enough things collected on the list, I put in and order to offset the shipping. It's nice being 1 day ground shipping away from McMaster-Carr. Almost as bad as Amazon prime. A little too convenient sometimes.
Box of bolts costs me about $5 to ship. I'd have that in gas running to Fastenal if I could get loose in time during the day to get there.
Just to tie this up, they are 10 mm x 1.5 (coarse) 45 mm long fully threaded flange bolts. Grade BH 9.8. McMaster PN 95735A645 is a zinc plated 10 mm X 1.5 45 mm long that is partially threaded 26-34 mm. Looking at the corrosion pattern on the bolts that should be fine. It is a class 10.9 flange bolt. ~$7 for pack of 10. If it won't work, I'll report back.
EDIT::
The above PN is wrong. I goofed and got fine thread by mistake. That PN is 10 mm x 1.25. The PN for coarse thread is 98093A636
They are the same as above except in black oxide and coarse thread. 10mm X 1.5 partially threaded 26-34 mm.