Bolts or machine screws

[glynn]

I have just ordered a fortunes worth of aluminium bronze for 6 chainplates for my Ed Burnett cutter, and am trying to source fastenings.
Ed specifies bolts, but half inch by four inch bolts are $10 dollars more expensive than half inch by four inch machine screws, and I need 18!!!
Even by my maths that makes 180 dollars.
Are there any differences in strength between machine screws and bolts if they are the same size?
Thanks in advance,

Glynn