There are 3 metal enforced holes & I needed a 4th. It?s a bit more intricate than it looks, but, it?s pretty good overall. I usually take a size 8 1/2 - 9 shoe and these were the only slippers I found which came in that size. I bought them to wear around the house after bunion surgery because Im not allowed to walk barefoot. After that, put earbuds back in the case. Great product and great service from the seller! You cant swap right and left. - it recognized that I use Siri and automatically connected, even though I dont think the optional software listed Siri as a voice assistant option (might have that confused w Bose, though). First off, the 12 bolts provided for the bar supports were too long to tighten down. I have purchased very expensive Clarks in the past, and these were every bit as good, if not better, and what an amazing price.