48 CFR §11.703

1. (a)The contracting officer shall insert the clause at 52.211-16, Variation in Quantity, in solicitations and contracts, if authorizing a variation in quantity in fixed-price contracts for supplies or for services that involve the furnishing of supplies.
2. (b)The contracting officer may insert the clause at 52.211-17, Delivery of Excess Quantities, in solicitations and contracts, when a fixed-price supply contract is contemplated.
3. (c)The contracting officer shall insert the clause at 52.211-18, Variation in Estimated Quantity, in solicitations and contracts when a fixed-price construction contract is contemplated that authorizes a variation in the estimated quantity of unit-priced items.