ZT Adapter – BSPT Female Cross

The ZT adapter is a BSPT female cross with four female taper ports arranged on two perpendicular axes. It brings four taper-threaded lines together at one point, which makes it a compact distribution block for supply, return, gauge and drain connections on the same machine. Because the ZT adapter has four taper joints instead of two or three, it also has four potential leak paths, and every one of them has to be assembled correctly the first time.

A cross is the densest way to join four lines, and that density is both its advantage and its risk. The body is small, the four ports are close together, and the internal cavity where all four bores meet is the point of highest local velocity in the fitting. This page explains the sealing and distribution behaviour, the complete dimension table, installation practice and the questions buyers ask most often.

1. What the ZT Adapter Does

A cross is a four-port fitting. In a hydraulic circuit it usually acts as a small distribution point: one port receives the supply, and the other three feed consumers, a gauge line, a drain line or a return line. It can also be used to bring two supplies and two consumers together, or to split a return line towards two tank connections.

The sealing principle is a taper thread on every port. A BSPT male thread is slightly conical, and when it is screwed into a BSPT female port the two thread forms interfere progressively along the engagement length. The seal is distributed over the thread flanks, so a thread sealant is required on the male thread and the joint must not be over-tightened. A cross body has four female ports cut into one small forging, so each port removes material close to the internal cavity; that is the main reason a cross deserves a careful torque discipline.

The four ports also interact hydraulically. When the flow enters on one axis and leaves on three ports, the internal intersection splits the stream, and the pressure measured at the gauge port is lower than the pressure at the inlet by the local loss in the cavity. On small crosses with high flow, that loss becomes significant, so the port that feeds the gauge should be chosen with the flow direction in mind.

2. ZT Adapter Specifications

2.1 Product Scope and Configuration

The range covers equal crosses in which all four ports share one thread size, from Rc1/8 to Rc1.1/4. The body is symmetrical, so the cross can be installed in any orientation and the port that faces the supply can be chosen on site. Reducing crosses with different port sizes on different axes are available on request; for a non-standard combination, send the drawing with the four port sizes and the required centre distances.

2.2 Materials and Surface Treatment

Standard supply is carbon steel with zinc plating for general hydraulic service. For corrosive fluids or aggressive atmospheres, 304 stainless steel or 316 stainless steel is available, and brass is offered for lower-pressure industrial and instrument lines. Plating options include trivalent chromium zinc (Cr3+) and zinc-nickel for a higher corrosion demand. No salt-spray hours and no plating thickness figures are published on this page; request the current test report from the supplier before a specification is frozen.

2.3 Threads, Standards and Sealing Principle

The thread column in the table covers ports E, F, G and H, which all share the same size in the standard range. The four ports are BSPT female taper threads to ISO 7-1, commonly written Rc. A taper joint seals on the thread flanks and needs a sealant such as PTFE tape or a liquid thread sealant applied to the male thread only. Because the seal depends on thread interference, a parallel 60 degree seat stud should not be used in an Rc port, since there is no cone inside the port for it to seat against.

2.4 Dimensions and Part Numbers

All dimensions are in millimetres. A, B, C and D are the four port lengths, measured from the centre of the body to the end face of each port, and S1 is the across-flats size of the body. In the standard range the four port lengths are equal.

2.5 Working Conditions and Limits

The usable working pressure of a taper-thread cross depends on the thread size, the body material and the quality of the male threads it is matched with, so no single figure covers the whole range. A four-port body carries more ports per unit of material than a tee, so the size and pressure combination should always be confirmed rather than assumed. For a specific project, state the fluid, the working pressure, the peak pressure, the temperature range and the vibration environment, and the supplier will confirm the suitable material, plating and assembly torque.

3. Part Number Decoding

The part number is built from the port sizes, written in the same order as the thread columns in the table.

• ZT-02: all four ports Rc1/8″X28.
• ZT-08: all four ports Rc1/2″X14.
• ZT-16: all four ports Rc1″X11.
• ZT-20: all four ports Rc1.1/4″X11.

A single size code means the cross is equal on all four axes. Where a reducing combination is requested, the drawing number replaces the standard code and the four port sizes are listed separately on the order.

4. Installation and Fitment

Because a cross concentrates four joints in one small body, assembly discipline matters more than it does on a tee.

1. Check that all four mating threads are BSPT male threads. A parallel thread will engage but will not seal.
2. Inspect the four female threads for burrs, corrosion and debris before anything is fitted.
3. Apply the sealant to the male thread only, leaving the first two threads clean so sealant is not pushed into the line.
4. Tighten each port in turn, holding the cross body on its flats so the torque is not carried by the ports already assembled.
5. Bring the four joints up progressively rather than finishing one port completely before starting the next.
6. Re-check the joints after the first heat cycle, and do not keep re-tightening a taper joint to stop a weep.

Where the cross feeds a gauge, fit the gauge on the port that sees the lowest flow velocity so the reading is not disturbed by the local loss in the body.

5. Applications and Industries

Typical applications include:

• Compact distribution points where four lines must meet inside a small envelope.
• Industrial power units: supply, return, gauge and drain connections at one point.
• Test benches: several measurement points fed from one junction.
• Mobile hydraulics: splitting a supply between three functions on the same machine.
• Marine and offshore equipment: stainless steel versions for continuous salt exposure.
• Mining and material handling: heavy bodies in high-vibration installations.
• Agricultural machinery: tapered joints where field service must use simple tools.

6. Replacement and Cross-Reference

When replacing an existing cross, work from measurements rather than from a colour code or an old marking. Record the four thread designations, the number of ports, the across-flats size S1 and the four port lengths. A replacement is equivalent only when the thread family, the port layout and the overall envelope all match. If the original part carries an unfamiliar number, measure the thread with a pitch gauge and send the values with a photograph so the equivalent can be identified.

A cross and a tee are not interchangeable, even when the port sizes are the same. Adding a fourth line to a junction that was designed as a tee increases the number of joints and changes the flow pattern, so the whole junction should be reviewed rather than extended.

7. Ordering, Packaging and Delivery

To place an order, provide:

• the part number, for example ZT-08 or ZT-16;
• confirmation that all four ports are BSPT female taper threads;
• the material and the plating option;
• the quantity and the required delivery date.

Parts are supplied individually protected and packed in bulk cartons or in kit bags, with the part number marked on the bag or the label. Minimum order quantities, carton quantities, marking and traceability requirements, and lead times are confirmed at the quotation stage, and special packing or kitting can be arranged for OEM programmes.

8. Frequently Asked Questions

Q1. What is the difference between the ZT adapter and a tee? The ZT adapter has four taper ports on two perpendicular axes, while a tee has three ports. A cross joins four lines at one point and saves space, but it also adds a fourth taper joint that can leak, so it should only be used where four lines genuinely meet.

Q2. Should I use a cross or two tees? Use a cross when the four lines must meet at one point and space is limited. Use two tees when the lines can be separated, because fewer joints per junction means fewer potential leak paths and easier service access.

Q3. Do I need sealant on all four ports? Yes. Every port is a taper joint and every taper joint needs a sealant on the male thread. PTFE tape and liquid thread sealants are both used, and the choice depends on the fluid and the site practice.

Q4. Can I use a parallel 60 degree seat stud in this cross? No. The four ports are taper female threads and there is no cone inside them for a parallel seat stud to seal against. Use a taper male fitting in every port.

Q5. Does turning the cross affect the pressure at the gauge port? Yes. The internal cavity splits the flow, and the port that faces the main flow direction sees a higher velocity and a larger local loss. Fit the gauge on the port that is least disturbed by the incoming stream.

Q6. Why is a cross more sensitive to over-tightening than a tee? Four female ports remove more material from a small body, so the wall around each port is thinner. Excessive torque wedges the taper thread and can crack the body instead of sealing the joint.

Q7. Which material should I choose for a marine application? 316 stainless steel is the usual choice for continuous salt exposure. 304 stainless steel suits many wash-down applications, and carbon steel with zinc-nickel plating is used where the environment is controlled and the cost target is tight.

Q8. How do I measure an unknown cross so I can order a replacement? Measure the outside diameter and the pitch of each female thread, then measure the across-flats size and the four port lengths. Send these values with a photograph and the supplier can identify the equivalent part.

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