UQD or UQDB: which quick disconnect fits hand-mate versus blind-mate liquid-cooled racks, and what changes in the machined parts?

What is the difference between UQD and UQDB in the OCP specification?

In the OCP UQD Specification v2.0.0 (2026), UQD is the hand-mate coupling, which needs direct manual intervention to couple and uncouple, and UQDB is the blind-mate coupling, which couples and uncouples indirectly through another mechanism. A hybrid joins a UQD plug to a UQDB socket blind.

The specification defines the plug as the half with exterior mating geometry and the socket as the half with interior geometry, in four sizes (02, 04, 06 and 08) for non-combustible single-phase water or glycol cooling loops. Version 2.0.0 combines the previously separate UQD and UQDB revisions into one document, with shared performance requirements across sizes and configurations. ASHRAE’s 2019 white paper describes the same split in plain terms: dry-break couplings that are connected manually through a latching mechanism (direct dock) or mounted on equipment with separate retention features (blind mate).

For an engineer picking one, the question is rack architecture. A hose that a technician connects at a server or manifold is a hand-mate joint. A server tray that slides into a rack and has to find its manifold port on its own is a blind-mate joint. The older Dasenic overview (January 2025), written when only the first revision of the hand-mate document was final, makes the same point: the two are related interfaces that should not be treated as the same mechanical requirement.

When should a design use UQD, UQDB or the hybrid?

Use UQD where a person connects the joint by hand and the latch gives feedback, UQDB where hardware slides into place and must mate blind with offset, and the hybrid only with an added compliance mechanism. The choice follows the rack design, not the machining.

The specification says hybrid applications should include additional compliance to account for overdrive and radial offset, and that overdrive devices are outside its cross-verification tests. For UQDB it tests force to connect at the maximum radial misalignment, and it advises keeping the approach angle to a minimum to limit wear on plug, socket housings and socket sealing. A blind-mate design therefore needs the rack or tray to hold alignment well enough that the connector’s own allowance is not the only thing absorbing tolerance.

On force, the specification states a maximum coupling force at zero pressure that applies to UQDB, and notes that the latch of a hand-mate socket is expected to add a little to the force to connect. The table compares the three configurations side by side.

How should the stud end, thread and hex be written on the drawing?

Reference ISO 11926-3 and the thread class by name, give the hex across flats as a toleranced dimension, and keep the O-ring seat and sealing face under the same finish and visual limits as the rest of the interface. Take the torque from the customer, because the table’s values are suggestions.

• Thread: call out the reference thread and the 2A class exactly as the customer names them (for example the 9/16-18 UNF-2A of an ORB-06 stud). The thread callout guide and the UNEF thread guide cover the notation, and the stud-end geometry itself belongs to the ISO 11926-3 standard, which is a paid document the drawing should reference by edition, not copy.
• Hex: the specification calls the hex size recommended, so the drawing sets the across-flats dimension and tolerance, plus the surface the hex sits on (Note 3 of the plug tables).
• Torque: the table gives suggested values from 9 Nm to 48 Nm across the stud ends in the specification, and its footnote says to consider mating geometry, material and lubrication. Stainless threads can gall under torque, which is covered in the stainless thread galling guide.
• Marking: the specification requires visible identification as UQD or UQDB with the size and a version suffix, such as UQD04 v2, on an external surface that is visible when unmated, and color identification for hand-mate parts. Put the marking location and method on the drawing; marking and any color treatment are arranged through partner plants that Saola manages.

For a part family running at ten to twenty thousand a year, fixing these items before the first quote avoids the usual loop of questions about which standard edition applies, who owns the torque value and which surfaces carry the finish limit.