Drue what long arm do you use if you don't mind me asking? Most long arms these days will accept just about any thread...and I don't see how a prewound could harm it. Worst case scenario you have a thread jam. Long arms are industrial machines...other than creating a mess with lint I don't know how you could damage it simply by using different thread. It is pretty standard practice to use different threads - different fibers and weights both - in the top and bobbin together...in both a domestic machine and a long arm.
Not being confrontational by the way...just curious!!
