What it is
The Zurn Wilkins 950XLT2 (successor to the 950XLT and the wye-bodied 950XL) is a lead-free bronze double check valve assembly in ¾" through 2". Its check covers sit at 45 degrees on top, so all four test cocks are reached from above and protected by plugs. Ball-valve shutoffs, union ends optional.
The envelope splits by size. On ¾" and 1" the underside is almost flat, ¾" below the pipe centerline, and the body stands 3⅜" above it. On 1¼" through 2" the body is symmetrical, 5⅝" to 6½" both above and below the pipe. Length runs 13" at ¾" to 21⅜" at 2".
What matters for the cover
Two envelopes. The ¾" and 1" units take the 20 × 20 and 24 × 24 closed-top covers with room to spare. The 1¼" through 2" units are both longer and deeper; the 30 × 24 is the closest fit at 1¼" and 1½", and the 2" at 21⅜" wants the 36 × 24 once you allow for the ball-valve handles.
Base closes fully. No relief valve, so close the cover to the pad. Ground heat stays in and wind stays out.
Top-access checks. The cover lifts straight off for service; nothing to unwrap.
Legacy 950XL. The older wye-body 950XL is shorter (11¼" to 18¼"). A cover cut for the XLT2 fits it loosely; the reverse does not hold.
Stocking
Where the utility allows a DC on irrigation, the 950XLT2 outsells the 975XL2 and its covers move in case quantities of the 20 × 20 and 24 × 24 through irrigation supply. Where an RP is required, the 975 takes over and shares the small covers. Add a few 30 × 24 and 36 × 24 for commercial 1½" and 2" services. The DCV covers page covers the category.