For provisions relating to the tax-free sales of articles referred to in section 4161(a) see:

(a) Section 4221, relating to certain tax-free sales;

(b) Section 4222, relating to registration;

(c) Section 4223, pertaining to special rules relating to further manufacture; and

(d) Section 4225, relating to exemption of articles manufactured or produced by Indians;

and the regulations thereunder.