In plain English
FAR 52.247-8, Estimated Weights or Quantities Not Guaranteed, is a contract clause prescribed at FAR 47.207-3(e)(2), most recently dated Apr 1984. The complete official text is reproduced below, verbatim, from GSA's published FAR source files.
Its text contains no sentence requiring insertion into subcontracts; see the flowdown section below for what that does and does not mean.
Does it flow down to subcontracts?
No flowdown mandate found in the clause text
We scanned the full clause text and found no sentence directing the contractor to insert this clause into subcontracts. That is a statement about the text, not legal advice: a prime contractor may still flow terms down contractually, an agency supplement (DFARS, VAAR, …) may add requirements, and clauses listed below (if any) may order this clause into subcontracts from the outside.
Where it's prescribed
As prescribed in 47.207-3(e)(2), insert the following clause in solicitations and contracts for transportation or for transportation-related services when weights or quantities are estimates:
Prescribing reference: FAR 47.207-3(e)(2).
The official text, verbatim
As prescribed in 47.207-3(e)(2), insert the following clause in solicitations and contracts for transportation or for transportation-related services when weights or quantities are estimates:
Estimated Weights or Quantities Not Guaranteed (Apr 1984)
The estimated weights or quantities are not a guarantee of actual weights or quantities, as the Government does not guarantee any particular volume of traffic described in this contract. However, to the extent services are required as described in this contract and in accordance with the terms of this contract, orders for these services will be placed with the Contractor.
(End of clause)