Bushings & Plugs

A selection of tapered- and parallel-thread fittings for cast iron radiators. We stock sizes to fit antique brands such as Gurney, American Radiator Company and Crane.

Showing all 3 results

Showing all 3 results

Using Thread Types To Date Sectional Radiators (Part 1)

Tapered Bushings On Pre 1970 Radiators

Cast iron radiators made before the mid 1970s had tapered right hand threads on the four openings. The photos adjacent show tapered-thread bushes, all of which were made before 1970.Use our tapered-thread Black Iron Bushings to replace these.

Using Thread Types To Date Sectional Radiators (Part 2)

Flanged Bushings On Sectional Radiators Made Post 1970s

Sectional radiators have used flanged, straight-thread bushes since the mid 1970s. This type of bushing forms a seal between the joining face of the outermost radiator section and the flange of the bushing by compressing a gasket in between the two. They are left hand thread on one side of the radiator and right hand thread on the other.Our new cast iron radiators use this kind of bush, as do those made by our contemporaries from the last fifty years.  The adjacent image shows parallel-thread bushes on radiators including our own and a model made in Italy until the early 2000s.If you have this kind of radiator, use our Forged Steel Reducing Bushings. You’ll also need the appropriate size gasket.

NPT: National Pipe Tapered

National Pipe Thread is the standard thread used on plumbing fittings across North America (but not in Europe, where BSP is the standard). Below, you’ll find tables showing NPT sizes in millimetres, an explanation of straight and tapered thread types and a handy thread size ruler and template to print out and use at home to check thread sizes. Our Printable Thread Size Template allows you to check the size of pipes, bushings or openings before ordering your components. Download Our Printable Thread Size Template

Nominal NPT Sizes In Millimetres

Nominal pipe size (NPT) Threads per inch Actual outside diameter, OD
inch mm
18 27 0.405 10.3
14 18 0.540 13.7
38 18 0.675 17.1
12 14 0.840 21.3
34 14 1.050 26.7
1″ 11-12 1.315 33.4
114 11-12 1.660 42.2
112 1112 1.900 48.3
2″ 1112 2.375 60.3
212 8 2.875 73.0

Tapered And Parallel Threads On Radiators

Parallel threads are used where the seal is made on a mating face. Most cast iron radiators have parallel threads and a gasket between each section.Tapered fittings achieve a tight thread-to-thread seal with the help of a little sealant such as PTFE tape.