I have a chandelier that came with a very thick insulation on the wires which were intended for use as a plugged in lamp. I am installing it as a chandelier, and it came with the mounting hardware, but the thick wires will not fit through the nipple very well. Is there some technique I'm missing? Even when I've got the thing forced through, twisting the nipple to screw it into the mounting bracket is impossible. And let's not even mention getting the wires to the right length.
Call the manufacturer for assistance or see if you can get heavy duty hardware at an electrical supply store. The included hardware may be low-grade & drilling the nipple hole more than a millimeter larger may cause a safety issue. The heavy duty stuff you can drill no problem, if needed. The canopy cover will likely then also need to be slowly drilled so a bigger nipple can fit through.