I used to work with leather - cutting, stitching, carving, and detail work.  Whenever you want to mold leather, you wet it, and it becomes more pliable.  Allow it to dry and the molding is set.  This is why this boot stretcher works.  This boot stretcher is heavy and very well built.  It did not come with instructions, so I was emailing back and forth with the seller, who could not forward an attachment to me because the seller said Amazon's policy wouldn't allow them to.  Anyway, I finally figured out that the long, thin bolt with the tee handle slides down and fits (by twisting it correctly) or locks into the lower part of the unit, which then responds to the turns of the tee handle - either making it wider or more narrow (spreading-wise).  Likewise, unlocking the bolt from the lower section (with the correct twist) and sliding the bolt straight upward as far as it needs to go to lock (with a twist) into the upper area of the device, will also respond to the turns of the tee handle and if you do a few turns to the upper, and return to the lower part and do a few turns there, then return to the upper part and continue, you can maximize how wide this device can spread.  So, we stretched a leather boot 4 inches and used the spray agent to make the leather more pliable but I think water or mist would also work.  But you can't just make the upper part really wide because the lower part also needs to be adjusted outward.

After I got the hang of this device, we were amazed!  No more ill fitting boots for us.  There are four females in this household who are boot lovers, and this device looks like it will last generations if used properly.  Before purchasing this, my daughter spent $50 to have a pair of boots stretched.  Highly recommended, but make sure you understand how to operate it properly.

Edit: I forgot to mention that I left the dampened leather boot on the stretcher for about two days.  I think it just needs to dry to set the stretched leather.