Here's a really easy project that helped me with a simple problem. Since I'm using a picnic cooler for a mash tun, I don't have a reliable way to measure my mash temp. I am uncertain exactly what water temp I need to set my HLT for to get the desired mash temp using a HERMS setup. The inline mash temp will go between the mash outlet of the HLT as it returns to the top of the mash. I can then set my HLT temp based on the output temp of the HERMS coil.
I am also finally going to break down and buy a plate chiller. Since I am using quick disconnects on this thermometer, I can also use it to measure the temp of the wort as it exits the chiller. I can then measure my water flow accordingly.
There are 4 parts in my configuration; a 1/2" mpt thermometer, a 1/2" stainless T, a 1/2" mpt x male camlock fitting, and a 1/2" mpt x female camlock fitting.
<a href="http://brewingsite.com/wp-content/uploads/2012/07/010.jpg"><img class="alignleft size-large wp-image-186" title="DIY Inline Mash Thermometer" src="http://brewingsite.com/wp-content/uploads/2012/07/010-1024x768.jpg" alt="inline mash thermometer" width="584" height="438" /></a>
Install took less than 5 minutes, just had to thread all the parts into the T.
<a href="http://brewingsite.com/wp-content/uploads/2012/07/011.jpg"><img src="http://brewingsite.com/wp-content/uploads/2012/07/011-300x224.jpg" alt="" title="DIY inline thermometer to measure mash temps on a herms system" width="300" height="224" class="alignleft size-medium wp-image-187" /></a>
Here is a shot of it mounted on the ghetto HLT.
<a href="http://brewingsite.com/wp-content/uploads/2012/07/013.jpg"><img src="http://brewingsite.com/wp-content/uploads/2012/07/013-300x224.jpg" alt="Ghetto electric HLT with inline thermometer to measure exiting mash temp" title="Ghetto electric HLT with inline thermometer to measure exiting mash temp" width="300" height="224" class="alignleft size-medium wp-image-188" /></a>
Total cost for this project was around $39. You could change the input and output connections if you are not using camlock fittings. It would be very easy with a triclamp setup as well. Just get a triclamp T, 1/2" female mpt x 1 1/2" triclamp adapter, and a thermometer, then clamp it all together.