Value hardware . I think Home Depot or Lowes would have it, I think its 1/4 inch. I layed the eggcrate on it as a guide and dotted it with a sharpie for evenly spaced holes., one for each 4 eggcrate squares, nmarked at th intersection of the cross, just enough to accomodate a plug surface Then clamped it and drilled/melted it with an ordinary spade bit. It was tedious as each 24 inch by 10inch piece has about 90 holes or so.