Your rack deserves the best.
If you are a pro you don't need my advice, you know what you'll do. But for the rest of us who build a rack I'll tell you that, this set is a must for your rack.
You have spend a lot of money to buy audio hardware devices, you want the best for your sound so the last thing you want is hum from ground loops created between 19" devices via the metal rails.
Here comes the "Adam Hall 5635 Humfrees M6".
Consists of (4) M6 screws, (4) Insulators and (4) Spacers this is a set for one device. In a very good quality it'll give insulation to your rack against ground loops and protection to the front panels of your devices against assembly damage. Also looks nice aesthetically.
Coming in a good price, don't even thinking to don't make this buying.