What are the hole spacing dimensions for the Linear Guide Rail 20mm? I'm trying to figure out what size aluminum extrusion to purchase so I can mount these to it.

Our SBR20 rails use M8 bolts and are suitable for use with 8020 aluminum or any other common machine material. We suggest the use of our ball bearing pillow blocks with these rails, which you can find on our website here: https://buildyourcnc.com/item/mechanical-rails-linear-ball-bearing-block Additional Information: HOW TO FIND WIDH 38 HEIGHT 26 LINER GUIDE RAIL