Thermafin pre-drilled headers are produced from straight length copper tube per ASTM B 88-current, Standard Specification for Seamless Copper Water Tube. UNS No. C12200, DHP (Phosphorized, high residual phosphorus), 1" Type M, H58 (drawn, general purpose) temper, full hard alloy.

A proprietary collaring bit is used to perforate and form vertical brazing surfaces at each hole along the length of the header tube.

The vertical brazing surfaces provide a large surface contact area to insure a thick, strong brazed tube to tube joint.

The cross-section, at right, details the brazed connection between the pre-drilled headers and the fintube.

According to the American Welding Society (AWS), the strength of the brazed joint will meet or exceed that of the ajoining tubes when the joint overlap and the depth of the filler metal penetration is a minimum of three times the thickness of the thinner base metal (tube), and a well-developed fillet is present.