Does the fulcrum of a 2nd or 3rd class lever have to be at the end? If so why? Here are the usual three classes of levers:

Source: http://mrtremblaycambridge.weebly.com/p15-turn/ing-on-a-pivot.html
Does the fulcrum of a 2nd or 3rd class lever have to be at the end? If so why? Why not have just a little bit more board beyond it? Why right at the end? 
 A: Speaking practically, it would make no difference the Fulcrum need not to be at the far end of the machine, to be a Second Class or Third Class Lever, as long as the Load is situated in between and Effort at the other end, that is the Effort Arm (distance between Fulcrum and Effort) is longer than the Load Arm (distance between Load and Effort) the Lever is a Second Class or if the effort is in between and load at the other end, then a Third Class Lever, in case any extra part is present beyond the Fulcrum in a second class or third class lever, that extra part is excluded or included in the Lever and does not make any difference.
Because, if we were to make calculations about certain quantities like Mechanical Advantage, Velocity Ratio, Efficiency of the lever, we would make calculations from the point at which the Fulcrum is located. Let us consider, the Fulcrum of a Second Class Lever is not situated at the far end but is somewhat away from the end. The Load is present in between. Now if we were to calculate the Mechanical Advantage of the Lever :-
Mechanical Advantage = Effort Arm/Load Arm------------(1)
Since it is proven both mathematically and experimentally that Mechanical Advantage (M.A.) of a Lever is equal to the ratio of its Effort Arm and Load Arm, we would try not to go much deep into the derivation of the equation. Now let us say that there is an extra part (F') beyond the fulcrum and we were to include that in making calculations of the M.A. of the Lever along with the presence of Fulcrum(F). So now the new Effort Arm after including the extra part (F') would be F'E and new Load Arm would be F'L. 
Calculating the new M.A. with F'E and F'L :-
M.A. = F'E/F'L 
In this case the extra part F' would simply become the new Fulcrum of the Lever, but since Mechanical Advantage is a ratio of the Effort Arm and the Load Arm and the common factor being the extra part (F') which we are considering in the Lever, the ratio of that Lever would come out the same and hence it will not affect its working. If we were to exclude the extra part F' from the Lever again we would get the original M.A. ratio and the working of Lever would be the same. Therefore we conclude that the presence of any extra board beyond the original fulcrum would not make any difference in the working of Lever and can either be included or excluded in making calculations about the Lever. 
