From the product description, check product page for current description, price and availability:

By popular request of an affordable sight gauge, we have added several economy sight gauges to our website. These are very easy to install in to a 7/8″ hole in your pot and will come with a full set of instructions. These sight gauges will fit most kettles up to 15 gallons, they are approximately 18″ from the center of the 7/8″ hole.
This sight gauge is a perfect addition if you want to make a dual purpose out of one hole for your ball valve and sight gauge.This sight gauge comes with the Stainless steel ball valve assembly

Sight Gauge Includes:

• 1/2″ MPT x 1/2″Compression Stainless Steel Fitting
• 18″ Poly-Carbonate Tubing
• SS Tee
• Set of Vinyl Graduation Stickers (2-15)
• Stainless Steel Close Nipple
•  Silicone o-ring
•  SS lock nut
• SS flat washer
• Optional Ball Valve Assembly

Optional Eye bolt allows you to attach the sight tube to your kettle, all you will need is a 1/4″ drill bit and drill to do this. We only offer a 4″ eye bolt for this sight gauge because it will be considerably further away from the kettle than our other sight gauges, this may not be long enough and you may want to wait until you install this and get a good measurement before you buy one. These should be available at your local hardware store as well.

Cleaning Your Sight Tube:
A simple occasional light cleaning with your favorite cleaner and a 3/8″ nylon hose brush is all you need to do. See option below if you don’t already have one.

If you are doing deep cleaning of more than 30 minutes, it is recommended to remove the sight gauge and install a hole plug during this cleaning period because extended contact of cleaning detergents could cause the poly-carbonate to crack.

Avoid direct flame contact and use a heat shield if necessary to avoid excessive heat to your sight gauge, the poly-carbonate tubing has a rating of up to 250 degrees. Paying attention to avoid both of these will increase the life of your sight gauge for many brews!