Standoffs can be many shapes and sizes and made of many different materials. those are made of metal. Insulating standoffs keep two parts from touching each other, thereby preventing an electronic short. Cable thumbscrews are often screwed into standoffs on the back of computers. Standoff sizes are usually measured by the Unified Thread Standard. Size 4-40 is used to secure cables to external computer ports and size 6-32 is used for motherboard mounts.  those are good for Arduino raspberry pi and electronic PCB separation

list of the Spacers dimensions:

Spacers • 10x M2.5 10mm Brass Female-Female
Spacers • 10x M2.5 12mm Brass Female-Female
Spacers • 10x M2.5 15mm Brass Female-Female
Spacers • 10x M2.5 6mm+6mm Brass Male-Female
Spacers • 10x M2.5 10+6mmmm Brass Male-Female
Spacers • 10x M2.5 15mm+6mm Brass Male-Female
Spacers • 10x M2.5 20mm+6mm Brass Male-Female
Spacers • 20x M2.5 8mm Stainless Steel
Screws • 20x M2.5 6mm Stainless Steel