Analysis of information sources in references of the Wikipedia article "Conversion (gridiron football)" in English language version.
For place kicks (field goal and convert attempts) the kicking tee platform or block can be no higher than one inch in height as per Rule 5, Section 1, Article 3 of the CFL Rulebook. For kickoffs, the ball may be held or placed on a tee such that the lowest part of the ball is no higher than three inches off the ground; Kicking tees are not required to be used. Kickers may kick off the ground if they desire.
The NFL allows the use of tees as high as 3 inches for kickoffs, but has never allowed them for field goals and PATs. The pro league, which began to declare its independence from the college game with a number of rules changes beginning in the mid-1930s, also has refused to widen the goal posts.
In the N.F.L., unlike college and the U.S.F.L., no tee is allowed on field goals.
