Female Plug Adapter 9C / 9D (Metric Female Cap for Male Cone Stud Ends)

Why the Female Plug Adapter 9C / 9D Is the Right Way to Cap a Line

The female plug adapter 9C / 9D is a cap that threads onto a male stud end and closes it. The sealing happens at the cone: the plug carries a metric female thread with a 24° cone seat, and when the plug is torqued onto the mating stud, the cone of that stud is pressed into the seat and the two steel faces seal. The line end is closed without a tapered plug, without tape and without a loose washer.

This is the part that keeps a machine clean during a build, a shipping, or an intervention. An open male stud end on a hose or tube assembly collects dust, swarf and moisture, and a cap that seals on the cone does the job without disturbing the cone itself. When the line is reconnected, the stud is cleaned and reused — nothing was cut, taped or glued.

The range is split into two series. 9C is the light L series and carries a 31.5 MPa pressure grade; 9D is the heavy S series with 63 MPa and 40 MPa grades across the range. Each part number is tied to a thread size and a tube outside diameter, so the correct cap can be selected from the table without measuring the stud.

Core Advantages

1. Seals on the cone, not on the thread — the female plug adapter 9C / 9D closes a stud end with a metal-to-metal 24° cone joint, so there is no tape, no paste and no washer in the joint.
2. No elastomer to age out — with no O-ring in the joint, the cap tolerates high temperature and long storage, which suits shipping and mothballing.
3. Removable without damage — the stud is cleaned and reused after the plug is removed, because nothing has been applied to the thread.
4. Sized by thread and tube O.D. — the table links each part number to a thread and a tube outside diameter, so the cap is selected by drawing rather than by trial.
5. Light L and heavy S series with published pressure grades — the 9C range carries a 31.5 MPa grade, and the 9D range carries 63 MPa and 40 MPa grades as listed.
6. Free cross-reference and 24-hour quotation — send the stud part number or a photograph and we will confirm the plug size and the grade within 24 hours.

Especificaciones técnicas

What Is a Female Plug Adapter?

A female plug adapter is a cap with an internal metric thread and a 24° cone seat. It threads onto a male 24° cone stud end and closes it. Unlike a pipe cap, which seals on a tapered thread, this plug seals where a tube fitting would seal — at the cone — so the joint behaves like any other connection in the same system, only with no line attached.

That is why the part is used on test ports, on spare branches and on assemblies being shipped. It closes a line end to the same standard as the fitting that normally occupies it, and it can be fitted and removed with the same wrench that the fitting needs.

The metric female plug adapter 9C / 9D therefore has one job, done properly: hold pressure at a capped stud end and let the stud be reused afterwards.

Connection — Metric Female 24° Cone Seat

Dimensional Data

Light L Series — 9C, 31.5 MPa Grade

Heavy S Series — 9D (63 MPa, 40 MPa and 31.5 MPa Grades)

The tables above are transcribed in full from the female plug specification drawing. The 9C light series runs from 9C-12 to 9C-52 with 9C-12 to 9C-22 at the 31.5 MPa grade and 9C-26 to 9C-52 at the 16 MPa grade, and the 9D heavy series runs from 9D-14 to 9D-52 with the 63 MPa grade on 9D-14 to 9D-22, the 40 MPa grade on 9D-24 to 9D-42 and the 31.5 MPa grade on 9D-52. Both are blanking plugs: they close a port, and the pressure they hold is set by the plug body together with the cone seat of the mating male stud, so they must not be treated as a load-bearing blind flange or used to blank a pressurised vessel opening.

Materials and Finish

Working Pressure and Operating Envelope

The pressure grade of a female plug adapter 9C / 9D is stated per part number: the light L series is listed at 31.5 MPa, and the heavy S series is listed at 63 MPa for the smaller sizes and 40 MPa for the larger ones, exactly as the specification table shows. Because the plug is a solid component with no bore, the limit is normally set by the grade of the mating stud and the port rather than by the plug itself; the grade is nevertheless quoted per size so that the cap never becomes the weakest element in a capped system.

Temperature behaviour follows from the metal-to-metal cone. With no elastomer in the joint the plug is limited by the stud and the fluid, not by a seal compound, which is one reason it is used on lines that are stored or transported rather than operated.

Where Female Plugs Are Used

The female plug adapter 9C / 9D is specified wherever a male stud end has to be closed:

• Spare branches and future expansion points on tube runs and manifold assemblies
• Ports and line ends opened during a machine intervention, then left closed
• Shipping and storage of hose and tube assemblies, so that internal surfaces arrive clean
• Pressure testing and flushing, where a line has to be blanked temporarily and reopened
• Service kits, where a small set of caps covers several tube sizes

In each case the objective is a closed line end that can be opened again without repairing the stud.

Installation Notes for the 9C / 9D Female Plug

1. Inspect the stud cone first. Look for dirt, burrs and paint. A metal-to-metal cone will not seal across damage.
2. Clean and dry the thread. Do not apply tape or paste; the joint is designed to seal at the cone.
3. Start the plug by hand until the cone contacts the seat. Starting a cone joint with a wrench is how threads and seats get damaged.
4. Torque to the value for the thread size and the stud material. More torque does not produce a better seal on a cone; it distorts the seat.
5. Pressure-test capped lines before transport or before the machine returns to service, particularly where the plug will be in place for a long time.
6. Clean the stud before reconnection. Remove any storage grease or debris, inspect the cone, and refit the line with a new torque check.

Quality, Testing and Traceability

Every female plug adapter 9C / 9D is machined from controlled steel stock, and thread form, seat angle, seat depth and hex squareness are checked as part of the normal production flow. Batch labels allow a supplied plug to be traced back to the material lot, and material test reports, dimensional inspection records and third-party inspection arrangements are available on request. OEM laser marking of part numbers or customer references can be applied where the quantity supports it.

Ordering Information

To order, specify four things:

1. PART NO. — from the 9C or 9D table, which also fixes the series and the pressure grade
2. Thread and tube O.D. — for confirmation against your stud drawing
3. Material — carbon steel as standard, or stainless steel to order
4. Quantity and marking — including any customer reference that has to be laser marked

Standard sizes ship from stock; non-standard threads and sizes above the tabulated range are machined to order.

FAQ

Does the female plug adapter 9C / 9D need an O-ring? No. The 24° cone is the sealing surface. Adding an O-ring or a washer prevents the cone from contacting its seat and creates a leak path.

What pressure grade will I receive? The grade is fixed by the part number and the size: 31.5 MPa for the 9C light series, and 63 MPa or 40 MPa for the 9D heavy series as listed in the specification table.

Can I reuse the plug after it has been in service? Yes. Inspect the seat, clean the thread, refit and torque. There is no sealing element to replace.

Will the plug protect the stud while the line is stored? Yes, and that is a common use. The plug closes the line end and keeps the cone and the bore clean until the line is reconnected.

Can you supply a plug for a size not in the table? Yes. Send the thread size, the tube outside diameter and the wrench clearance available, and we will machine a plug that fits.

Request a Quote for the Female Plug Adapter 9C / 9D

Send us the stud part number, the thread size or a photograph of the cap being replaced, and we will confirm the PART NO., the grade and the lead time within 24 hours. Please state the size, the material you require and the quantity, and tell us whether the caps are needed as a standalone service item or as part of a kit with the fittings and lines they protect. Standard sizes ship from stock.

Browse the full Hydraulic Adapters range for the complete family, or contact us to request a quote, mill test reports, and samples.