Speaker jack question

[mytool4u]

I have a 1/4 speaker jack in front of me and for the life of me I can't figure out which end is pos and which is neg. One of the posts has a rounded off end and the other has a squared off end. I know this is probably a no brainer, but I haven't done this in years. Thanks, here is a pic of the jack in question.

 

[Brion55]

The lug that goes to the "tip" of the 1/4" jack is +, the lug going to the sleeve is -