In plain English
FAR 52.247-19, Stopping in Transit for Partial Unloading, is a contract clause prescribed at FAR 47.207-6, 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 47.207-6 (c)(5)(ii), insert the following clause in solicitations and contracts for transportation or for transportation-related services when multiple shipments are tendered at one time to the contractor for transportation from one origin to two or more consignees along the route between origin and last destination:
Prescribing reference: FAR 47.207-6.
The official text, verbatim
As prescribed in 47.207-6 (c)(5)(ii), insert the following clause in solicitations and contracts for transportation or for transportation-related services when multiple shipments are tendered at one time to the contractor for transportation from one origin to two or more consignees along the route between origin and last destination:
Stopping in Transit for Partial Unloading (Apr 1984)
When multiple shipments are tendered at one time to the Contractor for movement from one origin to two or more consignees along the route between the origin and the last destination, the rate charged shall be the rate applicable to the aggregate weight, plus a charge of $______ for each shipment unloaded at an intermediate point en route to the last destination.
(End of clause)