As per photos

Label on box they came from "Steel Machine screws zinc Pozi 5/8 x 5/32"

Quantity 450 screws

checked the thread with a tap and die set. The 5/32w32 die fitted perfectly and wound all the way to the head with no resistance. (Note die nut not included) Found an article about Meccano bolt sizes excerpt below

"The screw sizes in question here are a British standard, and an American standard. Meccano uses the 5/32 BSW thread (for nearly all purposes). This is 5/32inch diameter (nominal, or 0.1563 inches) British Standard Whitworth: 32 threads per inch, a 55degree angle, and rounded top and root. (Inch measurements are given throughout, because all of the data I have is in inches.) This thread is not a common size (at least today in the USA), and many references do not list BSW data for the 5/32” diameter. The American thread is a #7-32, or a #7 (nominal) diameter (0.151”) and 32 threads per inch (also an uncommon size today). This uses the US Standard (or A. S. M. E. Standard) thread shape, which is a 60degree angle and a truncated (flat) top and root. From these dimensions, it might appear that measuring the outside diameter could resolve what the screw size is, but tolerances make this quite inaccurate. The diameter of the US screw is only 0.0053” smaller than the BSW screw. "

Pickup is from Cashmere.