The presses are to introduce pulleys or other parts and the extractor is to remove pulleys, rollers and other pieces depending on the type, if you want to mount the pulley you can heat it so that it dilate calze on the shaft.
If I want to take out and replace ... you decide to heat it to take out ... and as I put it back to colocat
To remove you need the extractor and to introduce the pulley is placed on a grill with fire so that the piece to be placed is dilated, in my beginnings I extracted the pulleys by placing 2 tubes between 2 partitions so that the pulley will hang and hit the shaft With a wood and brown.