4B BSP Male 60° Seat or Bonded Seal Plug Adapter — 4B Adapter for Capping Spare Ports

1. What a 4B Adapter Does

The 4B adapter is a single-ended BSPP male plug that closes a hydraulic port which is not in use. Its stud end carries a G (BSPP) parallel thread to ISO 228-1 and screws into a BSPP port on a manifold, valve block, pump, cylinder, accumulator or filter head. There is no second line connection, because the purpose of the part is to close the port rather than to join two lines.

A plug has only one interface, so that interface decides everything. The thread form, the thread size and the sealing surface of the plug must match the port exactly, because that single joint is the only barrier between the fluid system and the atmosphere.

Series 4B is a double-use plug. It seals against a 60° cone seat when the port has an internal cone to ISO 1179, and it seals against a flat face with a bonded seal washer when the port face is flat. One part number covers both port styles, so a maintenance store can hold one plug instead of two.

2. 4B Specifications

2.1 Connection 1 — BSPP male stud end (into the port)

• Thread standard: ISO 228-1 parallel pipe thread, G series. This is the port thread family used by ISO 1179 hydraulic ports.
• Gender: male.
• Size range: G1/8″x28 up to G2″x11, ten sizes in the standard table.
• Sealing: 60° cone seat or bonded seal washer, depending on the mating port.
• Mating port: a BSPP port machined to ISO 1179 with a 60° internal cone, or a flat-faced BSPP port that takes a bonded seal washer.

2.2 Connection 2 — closing head (no line connection)

• Function: the head closes the stud end and provides the drive for tightening.
• Drive: external hex, dimension S1 in the table.
• Sealing face: the underside of the head carries either the 60° cone seat geometry or the flat shoulder that the bonded seal washer sits against.
• Mating part: none. The head is not connected to any hose, tube or fitting.

2.3 Construction and Materials

The body is machined from bar stock on CNC lathes. Standard material is carbon steel with trivalent chromium zinc plating (Cr3+) for general hydraulic service. Zinc-nickel plating, 304 stainless steel and 316 stainless steel are available for corrosive and offshore duties, and brass is available for selected sizes. The bonded seal washer, where used, is supplied in NBR, FKM or EPDM according to the fluid and temperature of the application.

2.4 Pressure and Temperature

Working pressure is not fixed by the part number alone. Pressure is governed by the thread size, the wall thickness of the plug, the sealing method used at the port and the body material, so working pressure for these sizes is confirmed per order by HENGHUA engineering, based on the sealing method, thread size and material selected. Seal material temperature limits apply as material facts: NBR approximately -30°C to +100°C, FKM approximately -20°C to +200°C, EPDM approximately -40°C to +120°C.

2.5 Part Number and Dimension Table

Every value below is taken from the published series chart. All dimensions are in millimetres. A is the thread length of the stud end, L is the overall length of the plug, and S1 is the hex across flats of the head.

Note on thread notation: a designation such as G1.1/4″x11 means a 1 1/4 inch BSPP thread with 11 threads per inch. The number after the x is the thread pitch in threads per inch.

3. How to Read a 4B Adapter Part Number

A 4B part number has a fixed structure: series prefix, size code, and an optional suffix.

• 4B is the series prefix. It identifies a BSPP male plug with a 60° cone seat or bonded seal, the single-ended plug of the British Adapters range.
• The two digits are the size code, and they are the nominal bore in sixteenths of an inch. 02 means 2/16 inch, which is 1/8 inch; 04 means 4/16, or 1/4 inch; 08 means 8/16, or 1/2 inch; 16 means 16/16, or 1 inch; 20 means 20/16, or 1 1/4 inch; 32 means 32/16, or 2 inch.
• The suffix marks a variant of the same plug. The 4B-WD series uses the same threads and adds a captive seal; that series is ordered under its own part numbers.

Worked example from the table: 4B-08. The prefix 4B tells you it is a single-ended BSPP plug for a 60° seat or bonded seal port. The code 08 gives a 1/2 inch nominal bore, so the thread is G1/2″x14. Reading across, the thread length A is 16 mm, the overall length L is 26 mm, and the hex across flats S1 is 27 mm, so the port opening must clear a 27 mm hex plus the swing of the wrench.

4. Installation and Fitment

Fit the plug by hand for the first turns, then tighten with a wrench on the hex until the sealing face contacts its seat. Tighten to snug contact and stop; BSPP threads seal at the cone or at the washer, so additional rotation does not improve the seal and can distort the washer or cold-work the thread. Tighten a BSPT plug differently, since a taper thread seals on the thread flanks and needs a thread sealant.

Before fitting, inspect the port for burrs, swarf and old sealant. A bonded seal washer must sit square on the flat face with no debris trapped underneath. Check the cone seat for scores and for the correct 60° angle. Keep the plug and the port clean during assembly, because a single chip at the sealing face produces a weep that looks like a thread fault.

Common fitment errors and their symptoms:

• Cross-threading the plug into an aluminium or cast iron port. Symptom: the plug stops hard well before the head reaches the port face.
• Using a 60° cone plug in a flat-faced port with no bonded seal washer. Symptom: leakage at the head despite full tightening.
• Reusing a crushed bonded seal washer. Symptom: a slow weep after the first thermal cycle.
• Fitting a taper thread plug into a parallel port, or the reverse. Symptom: the plug enters a few turns then binds.
• Over-tightening a small size in a soft material. Symptom: a stretched or cracked port boss.

Treat bonded seal washers as single-use items and replace them whenever a plug is removed for service. Plugs themselves may be reused after inspection of the thread and the cone or shoulder face.

5. Applications and Industries

Typical applications and industries for this plug include hydraulic systems, water jetting equipment, oil and gas service equipment, industrial machinery, construction machinery, agriculture, marine hydraulics and material handling equipment.

Four concrete uses:

1. Capping a spare port. A manifold or valve block is supplied with more ports than the current build needs. This plug closes the unused ports so the block can go into service without a blank flange or a plugged hose.
2. Isolating an unused branch. During a machine rebuild, a circuit branch is removed but its port remains. A plug isolates that branch from the rest of the system.
3. Capping a line during commissioning. On a test bench, sections of a circuit are run one at a time with the other ports closed, which lets the technician pressure-test a sub-circuit while the rest of the machine stays assembled.
4. Protecting a port during transport. Pumps, cylinders and blocks are shipped with their ports closed to keep out moisture, dust and insects and to prevent damage to the seat during handling.

6. Replacement and Cross-Reference Guide

Identify a replacement plug by standard and sealing method, not by the source of the original part. BSPP port threads are defined by ISO 228-1 and the port sealing geometry by ISO 1179, so any plug that matches the thread and the seat serves the same function. Where a machine uses several pipe thread families, separate the families first: BSPP (parallel, G) to ISO 228-1, BSPT (taper, R) to ISO 7-1, JIS gas thread to JIS B 0203, and the metric and SAE families to their own standards.

Measure these three things before ordering:

1. The thread. Measure the outside diameter of the male port thread with a caliper and compare it with the size code table, then check the pitch with a thread gauge. A parallel thread measures the same diameter over its whole length; a taper thread gets smaller toward the end.
2. The seat. Look into the port. A machined 60° internal cone means a cone seat plug. A flat machined face with a spot face around the thread means a bonded seal plug. A port with a machined counterbore for an O-ring is a different family and needs a different fitting.
3. The space and the drive. Measure the clearance around the port and compare it with the hex S1 and the length L of the plug you intend to fit. Where the clearance is tight, the hollow hex versions of the plug families allow the use of an internal hex key instead of a wrench on an outside hex.

7. Ordering, Packaging and Delivery

To place an order or request a quotation, send the series code, the full part number, the thread size, the seal material, the plating or material grade, and the quantity. Example: 4B-08, G1/2″x14, carbon steel with trivalent chromium zinc plating, bonded seal washer in NBR, 500 pieces. If a size or a thread combination is not in the published table, send the drawing or the mating port dimensions and HENGHUA will quote it as a special.

Plugs are packed in sealed polyethylene bags inside cartons, with the part number, thread size, material and quantity printed on the label. Bulk cartons and labelled shelf packs are both available for distributor stock. Sample orders are accepted for validation before a production order. Lead time is confirmed per order, since it depends on the size, the material grade, the seal selection and the order quantity.

8. FAQ

Q1. What is the difference between BSPP and BSPT, and can they be interchanged? BSPP is a parallel pipe thread to ISO 228-1, where the pressure-tight joint is not made on the threads themselves; sealing comes from a 60° cone seat or a bonded seal washer. BSPT is a taper pipe thread to ISO 7-1, where the joint is made on the threads and a sealant is required. The two are not interchangeable: a parallel plug in a taper port leaks, and a taper plug in a parallel port damages the thread.

Q2. What is the difference between a 60° cone seat and a bonded seal, and which should I choose? A 60° cone seat seals metal to metal between the cone of the stud end and the cone of the port, as defined for BSPP stud ends in ISO 1179. A bonded seal washer seals against a flat face, with the elastomer bonded to a metal washer. Choose the geometry your port is machined for: check for an internal cone, or for a flat spot face. This series is a double-use plug, so it suits both port styles; a plug for a flat-faced port must have a washer fitted.

Q3. How do I identify the correct 4B adapter size? Measure the outside diameter of the male port thread and match it to the size code table; the two-digit code is the nominal bore in sixteenths of an inch, so 08 is 1/2 inch and the thread is G1/2″x14. Confirm the pitch with a thread gauge and confirm clearance for the hex S1. If the measured diameter falls between two table sizes, the port is probably another thread family and should be identified against that standard.

Q4. What seal material should I select for my fluid and temperature? NBR suits mineral hydraulic oil and general service at approximately -30°C to +100°C. FKM suits higher temperatures and aggressive fluids at approximately -20°C to +200°C. EPDM suits water, water-glycol and steam service at approximately -40°C to +120°C, but is not the first choice for mineral oil. Match the elastomer to the fluid first and to the temperature second.

Q5. How is the working pressure of this adapter determined? Working pressure is governed by the thread size, the wall thickness of the plug, the sealing method at the port and the body material, so it is not a single figure for the whole series. Working pressure for these sizes is confirmed per order by HENGHUA engineering, based on the sealing method, thread size and material selected.

Q6. What is the minimum order quantity and can I get samples? Sample orders are accepted so that a plug can be validated against the actual port before a production order is placed. Minimum order quantity depends on the size, the material grade and the seal selection, and is confirmed with the quotation. Send the part numbers and the expected annual volume so that the quotation covers both the sample and the production batch.

Q7. Can a 4B adapter be reused after it has been in service? Yes, if it is clean and undamaged. Inspect the thread for deformation, check the 60° cone or the flat shoulder face for scores and corrosion, and confirm that the hex is not rounded. Replace the bonded seal washer, since the elastomer takes a permanent set after the first tightening. Seal washers are treated as single-use parts.

Q8. What is the difference between a solid hex plug and a hollow hex plug? A solid hex plug is driven by a wrench on the external hex S1. A hollow hex plug, such as the 4BN-WD series, is driven by a hex key in an internal recess and keeps the same external thread. The hollow hex version is used where the space around the port is too small for a wrench, or where the plug must sit lower in the casting.

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