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Sandwich Plate Centre Bolts

Sandwich Plate Centre Bolts
Details:
A sandwich plate centre bolt is the load-bearing core of any oil-cooler sandwich plate kit. Where an ordinary bolt simply clamps two parts together, this component does double duty: it holds the plate against the engine oil filter head while a hollow through-bore carries engine oil out to the cooler and back. KEY-CNC (Shenzhen Feimoshi Technology Limited) has machined custom fasteners and precision parts since 2008, supplying OEM and performance-market centre bolt kits from its Shenzhen facility for automotive, motorsport and marine applications.
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Description
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product-559-559

Uniqueness of Centre Bolts

Oil routes differ. Stock oil-filter housings send oil from the pump to the filter cartridge and back into the galleries. That flow must be interrupted, diverted through an external chiller, and returned when a sandwich plate is inserted. The central bolt permits this. An axial through-bore of controlled diameter lets engine oil enter the male end, pass through the hollow shaft, and exit the plate internal galleries, where the cooler lines join.
Typical sandwich plate centre bolts are three-zone. Male thread meets oil filter head (M20 x 1.5 is usual, with 3/4"-16 UNF on US-built engines), hex body gives wrench access, and female bore thread receives cooler adapter, AN fitting, or sensor port. Male and female threads share an axis, hence they are cut together for concentricity. The bore misalignment creates unequal O-ring compression and oil-flow turbulence at high engine rpm.
The plate groove is filled with the O-ring, the plate is moved to the filter head, and the bolt is torqued to compress the seal evenly without crushing it. Overtightening alters the bore and oil-flow cross-section, therefore torque matters more than on a structural bolt. Since KEY-CNC prints torque and tightening on the kit drawing, installers get consistent results.

 

 

 

Threads, Through-Bore and Material Options

Every custom bolt in this family starts from a small set of decisions: thread pattern, bore diameter, length and material. The table below covers the typical envelope for KEY-CNC machines:

Specification

Typical Range / Option

Male thread

M20 x 1.5, 3/4"-16 UNF

Female thread

M20 x 1.5, 1/8"-27 NPT, AN -10

Overall length

40-60 mm

Hex size

22-25 mm

Through-bore diameter

6-10 mm

Material

Zinc-plated 1045 steel, 304/316 stainless

Material choice follows the operating environment. Zinc-plated carbon steel is the cost-effective default for street and track use, offering good strength and adequate corrosion resistance under the bonnet. 304 stainless steel is preferred where salt, humidity or long service intervals matter - coastal cars, marine engines and restorations - because it survives without plating. KEY-CNC holds male thread geometry to DIN 13 (6g) tolerances, verifies the bore with air gauging, and supplies material certificates per batch on request. Sealing grooves can be added in the same way as the O-ring grooves cut on our ATF drain bolts, keeping the fluid path clean and repeatable.

 

 

Fluid Integrity, Sealing

A square or circular O-ring between the sandwich plate and the filter head seals the plate-to-engine interface, and the bolt compresses it equally along its circle. Deburring every cross-drilled port prevents flash from entering the oil circuit after KEY-CNC manufactures the sealing face flat and perpendicular to the thread axis. For high-pressure or AN-fitted builds, the female thread is cut with a regulated chamfer to seat the adapter squarely and verified for concentricity before shipment. The joint is leak-free and thermally stable from cold start to track use.
We ensure thread quality with consistent tapping and gauging across our fastener range, and the bore finish (Ra 0.8 µm or better) maintains oil flow and prevents debris buildup.

 product-1024-559

 

 

 

Where Sandwich Plate Centre Bolts Are Used

These centre bolts appear wherever an external oil cooler, thermostat or sensor must be added to an engine:

  • Performance and track cars: mounting a remote oil cooler with AN -10 lines and a thermostatic plate.
  • Sensor installation: 1/8" NPT ports in the plate let oil temperature and pressure sensors read the main gallery directly.
  • Marine and coastal fleets: stainless centre bolts resist salt corrosion where plated steel would fail.
  • Prototype and racing engines: custom bore diameters, lengths and thread combinations machined for one-off builds.

Where the plate itself carries hardware-inserted fittings or sensor bosses, the same Shenzhen facility can machine the complete sandwich plate kit - plate, bolt and sealing rings - so thread, bore and port geometry stay matched from one source.

 

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