Posted 2019-June-01, 18:51
In the US, it's rare for an opening 2 M to be anything but 1 suited.
In 1st or 2nd seat, it's almost always a 6 card suit. However, in 3rd seat, anything goes. The only limiting factor in 3rd chair is what players who play a Drury variant would open 1 M on.
But beyond suit length, there are differences in how "good" the weak 2s are in terms of quality and strength. At one point, the ACBL had enacted the "Bergen" rule which required at least a 5 card suit with 5 HCP in the hand for a weak 2 M. That was to reign in American expert Marty Bergen who would weak 2 on virtually anything.
But different partnerships can have vastly different ways they open 2 M in 1st or 2nd seat that align with their general approach to bidding
-- A few still cling to a conservative approach -- 3 honors, top of range, etc.,
-- Most people probably use a little more aggressive opening with something like KJ9xxx or better and be willing to shade the HCP some with the right hand, and,
-- Some will consider a Jxxxxx and 5 HCP a normal weak 2 M.