adaptor studs for speaker spikes needed

I recently bought a couple of amp stands that came with these really cheesy cheap spikes. The stands are threaded for a 5/16-18 and the spikes I have and want to use are threaded 1/4-20. Any ideas as to where I kind find some adaptors that have male 1/4-20 threads to a 5/16-18 male threads??? I know that I can tap the spikes out to a 5/16-18, but that is my last resort. I know that Polycrystal sells the adaptors that I am looking for, but Polycrystal wants an arm and a leg for anything and everything. I've already checked the web sites for MCM Electronics and Parts Express with no luck there. Any info would be a great help. Thank you.