What is the best type of nail or tack to fasten the treads to wooden stairs? Thank you!

They won't tell you but with some proper measuring and a little patience, you can use two sided indoor carpet tape. Less mess if you're not used to using the adhesive because that can be a mess if you're unaccustomed to it which creates a bigger problem than it solves. Just be sure if using the tape, your suface is VERY clean and on the nose of the step you may have to trim a small bit of the overhang off. Hope this somewhat helps. I've done remodeling for years, have used this method several times never having any complaints.

Thank you for your question! Typically we recommend cove base adhesive or staples for this stair tread.