These are machine shop tools that offer different methods of holding a work piece at a desire angle.   

Professional shops use standard sized 5 inch and 3 inch sine bars to set precise angles. (In order to use sine bars you need to have gage blocks, see instructions tab for how to use.)   

The angle block set is a quick alternative method of setting an angle.The triangle blocks have the angles 5 degrees, 10 deg, and 30 deg which can be stacked to give you any angle between 5-45 deg, in 5 deg increments. (Place blocks in reverse to subtract angles). The J shaped holder keeps them from sliding off of each other.  

Steel Sine bar on amazon for reference: http://amzn.to/28OzfdX