Here's more information on the Onyx forge kits from the man himself (I sent him a link to my installation on Kasmir here on the board and here's his reply):
Hi Trevor -
Nice job - I think you'll find that your new axe has plenty of sustain. By the way, any minor vertical alignment differences between screws is rectified when the neck is snugged up to the body and the inserts fully seat themselves.
What I like about this particular set of neck kit components is that they are somewhat forgiving regarding alignment, yet are strong enough to provide over 1,600 lbs of clamping pressure between the mating neck / neck pocket surfaces.
Remember that when you tighten those screws down not to over do it, as the same amount of torque provides much more clamping pressure when utilizing metal to metal connections with machine threads as compared to wood screws.
Best regards, and thank you for the feedback.
Roy Bullis
Onyx Forge Custom Guitars LLC
www.onyxforgeguitars.com
These inserts are zinc plated steel - and from my experience on three guitars they work great.