Corolla 1.4 2005 VVTI rear caliper bracket to back plate bolt size


My daughter got herself a little Corolla as titled to learn to drive with. The rear disk protetive backing plates were so rotten the handbreake cable went through it and minced the fittings. I've done a few of these over the years, and have purchased the kit to re-fit the brake shoes, but the bolts used to fit the caliper mounting bracket to the backing plate are so corroded they have rounded off. I tried welding a large nut in each without luck so I'm going to have to drill them out and get new ones.

Its a funny setup, part drum brake for parking and part disk brake for regular braking.

Can anyone tell me what size the bolts are?
All I can find online is bolts for the caliper guide pins, but not for the mount itself.

Thanks in advance,