This is the famous Yo-Dave trigger tuning kit. 

There are several spring weights to adjust pull and also 4 colour coded shim tubes to adjust the sear engagement and also a replacement roll pin.

By experimenting with different springs and tubes and carefully testing that the rifle will not fire with a bump (i.e. hit with a rubber mallet or drop on the butt) you can get a light, crisp and safe trigger pull. 

The kit comes with illustrated instructions but I would suggest watching one of the clear and step by step instructional videos on Youtube. Just search "Yo-Dave trigger kit". 

In my experience the original Brno sears are quite smooth and the kit can be just fitted as is. My CZ 452 had some machining marks on the sear surface which I polished using 800 and 1200 wet and dry paper. No metal is removed in this process you just want a smooth surface.

These kits will give a nice safe trigger pull from a match grade light pull on a target rifle to a crisp but heavier pull on a hunting rifle. They are as good (and cheaper) as the replacement triggers such as Timney or Rifle Basix while keeping most of the original factory parts and do not require the removal of any wood from the stock.

Free Postage in Australia.