Hi Cheryl, first of all if you purchased the machine right off of the floor, then it probably was never set up to sew leather, it is probably an upholstery machine. A machine that is set up for leather, is set up differently. The presser feet are smooth,so they won't mark the leather, the feed dog is buffed to take off the sharpness off the teeth, so it won't mark the leather as well. and of course you will want to use a 135X16 TRI needle. In my 36 years of being a mechanic, this type of machine will not sew 277 thread on top unless the basket, or plate have been modified to do so. Even if you do modify the basket or plate, there is no guaranty that it will work. There is not enough clearance in that type of hook system to allow the 277 thread to clear. It will get hung up somewhere. I do not recommend modifying this machine. Use a 207 on top and a 138 in the bobbin, this is where you will get the best results. There is a misconception regarding sewing 3/8 inch leather. Just because machines are advertized to sew this thick, they are not able to use heavier thread,(346,277, and sometimes 207), you see, the problem is not the thickness of the leather, but in fact, the weight of the thread. This is why you shouldn't try to sew skirts on this machine, because to do so, you will only be able to use 207 thread(at the max), and 207 thread is not strong enough to hold a saddle together, it will compromise the integrity of the saddle, and it will not last long. Bottom line, you need a heavy duty machine for this type of work, and save this one for your light to medium weight leather. Call me if you want more info, 1-866-962-9880, thanks, Steve