Tip selection guide 
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Tips
Selection:
One of the most important aspects for successful solder removal is the
selection of the proper size tip. There are several points to keep in
mind.
1 The Inside Diameter (I.D.) of the tip must be large
enough to fit over the lead, while providing sufficient room so that air
and solder can be drawn through the tip.
2 The Outside Diameter (O.D.) of the tip must be slightly
smaller than the diameter of the pad to prevent tip contact to the board
laminate and minimize the possibility of damage.
