For Ranger School, this an optional item, but I recommend you bring one pair for every phase and one extra (4 pair). My logic behind this recommendation is that you'll likely lose two pairs of gloves during the course, especially if you recycle, and if you do you'll still have one extra pair for your battle buddy who lost theirs. That is what I did when I went through.
For Sapper Leader Course, this is a mandatory item and you are required to bring two. I recommend you bring three pair, because you will undoubtedly lose a pair, and if you recycle you don't want to restart the course with one pair of gloves. When I went I only brought two and when I recycled patrols I had to borrow a pair from my battle buddy.
For SFAS, this is a mandatory item and you are required to bring one. I recommend you bring two pair, because if you lose a pair you don't want to be without them.
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