They are Country pick up 13mm bolt thread size Expanding cooking leisure
Metric 13mm Broached-Hex Socket Head Shoulder Screws by UNICORP Metric/Standard-Stock/Custom, Slotted/Hex Socket Head-13 finishes/Stainless Steel/ Brass/ Carbon Steel- Official Site
Technical Information
How to read metric bolt charts - Quora
Aexit M6 x 1.25mm x 10mm Hex Bolts Tap Phillips Head Screws Fastener Silver Tone 20pcs (2dbc5999f9975bb34047b9a4cc6d009c) : Amazon.co.uk: DIY & Tools
Hex Bolts Dimensions Table | DIN 933 | DIN 931 Size Chart
Metric Bolt Measuring Guide | How to measure a Fastener | Pro-Bolt