The HLT is made from a 33L stainless steel stock pot.  These pots were relatively cheap off ebay, around £32, consequently the steel is a little thin <1mm.  The stockpot was modified to accommodate a ½ inch Stainless Steel ball valve and a 2.2KW heating element.  Two holes were drilled in the pots, one 20mm for the ball valve and one 40mm for the heating element.  Drilling the holes was a pain and I went through a couple of Bosch 40mm hole saws. Many other home brewers recommend the QMAX cutters.  The heating element was taken from a brand new Tesco Valve kettle, (cost around £5).
Although the pots are a little thin I’ve never had a problem with them.  The HLT is also equipped with a small dial thermometer and a temperature sensor that is connected to one of my PID controllers.

I have partly insulated the HLT using some foil backed bubble wrap. (wickes) I chose to use this method so I could easily remove the insulation when cleaning the HLT.

Inside the HLT -

As you can see there is a small kettle heating element, a couple of probes and the back of the ball valve. The longer probe is the dial thermometer. this is a very cheap (£3) thermometer purchased from www.thermometersuk.com

The smaller probe connects to the PID controller. This temperature sensor was purchased from www.auberins.com