The AIA Document A401™ is the Standard Form of Agreement Between Contractor and Subcontractor intended for use in establishing the contractual relationship between the contractor and subcontractor.
It spells out the responsibilities of both parties and lists their respective obligations, which are written to parallel A201™.
Blank spaces are provided on the A401 where the parties can supplement the details of their agreement.
In addition, the A401™ may be modified for use as a subcontractor-to-'sub'-subcontractor agreement.
As mentioned elsewhere, about another AIA form, this A401 may not be the best form for your needs. Before agreeing to use it, have it looked at by an attorney.