Those look hand made. Was he a wood worker? A peg board tray could have been used for anything. He could have used them for tool organization and the pegs were to keep tools/parts from shifting and rolling off if he was carrying the tray around the shop.
My opinion is your Grandfather was a very organized Wood Worker.
I noticed in the box holding this item, he may have had an Orbital Sander...I believe he may have had a Router also.
I also believe this tray was built to store his Router Bits?
With the number of them they could be for router bits if he had a lot of them or........they could be made for use when Crocheting , specifically a Blocking Board. Grandma might know also.