Removable tube heat exchanger with retaining assembly

A heat exchanger comprising:

• a first header plate having a tube side and a tank side;
• and
• a plurality of first apertures extending through the first header plate, each first aperture having a first portion on the tube side of the first header plate, the first portion having a first cross-dimension, and a second portion adjacent the first portion and having a second cross-dimension that is smaller than the first cross-dimension, and a first shoulder formed between the first and second portions;
• a plurality of flow tubes having a first end and a second end and a plurality of fins on an exterior surface thereof, a first end of one of the flow tubes being received in each of the first apertures;
• a plurality of collars, each collar having an aperture extending therethrough;
• at least one collar including a boss extending outwardly therefrom and having a beveled edge, the aperture of the collar extending through the boss, at least a portion of the boss having the beveled edge being received in the first portion of one of the apertures in the plate;
• a seal positioned in each of the first portions of the first apertures in the first header plate and positioned between one of the beveled edges of the boss and one of the first shoulders;
• and
• a fasteners extending through the collars to the plate.