The drilling decides the fit
Two flanges bolt together when the bolt circle, the number of holes and the hole size agree. The outside diameter helps to tell the standard, but the bolts follow the drilling.
Reference tool — not inspection
Identify the flange before it goes in an RFQ.
Flange measurement
Enter the dimensions you could take.
The bolt circle and the hole count are enough; the outside diameter and the hole diameter narrow the result. Below the examples, an offered flange designation (DN100 PN16, JIS 10K 100A, NPS 4 Class 150) can be checked against the reading. Each candidate also names the pipe of the same standard family and the ring gasket that fits. A spiral wound gasket shows its winding and filler as colours on the ring edge: read the colour code. The facing, flat or raised, is not part of the drilling: what to check.
Between the centres of two opposite holes; or choose edge to edge: from the outer edge of one hole to the outer edge of the opposite one, and the hole diameter is subtracted for you.
Examples:
Replacement check
Against your reading and the drilling tables alone: the drilling does not show the pressure rating or the facing, so check that the rating of the offered flange suits the system.
All 130 engineering tools
A valve, a pump or a strainer is ordered with flanges, and the flange standard is the detail most often missing from the request. JIS B 2220 is the Japanese flange standard, EN 1092-1 the European one and ASME B16.5 the American one; equipment usually follows the standard of the country where it was designed, and one ship can carry all three. Measure the flange, count the holes, and the tool lists the standard drillings that fit.
The drilling — bolt circle, number and size of holes — decides whether two flanges bolt together. It does not decide the pressure rating: several ratings share one drilling, and the tool groups them so that the measurement is not read as more than it is.
Why flanges get confused
Drilling, rating and standard.
Ratings share drillings
In EN 1092-1, DN50 has one drilling for PN10, PN16, PN25 and PN40, and PN10 and PN16 agree up to DN150. In JIS B 2220, 10K and 16K agree up to 40A. A measurement cannot give the rating.
Close, but not the same
JIS 10K 50A and ASME Class 150 NPS 2 differ by 2.6 mm on the outside diameter and 0.7 mm on the bolt circle, with four holes of about 19 mm on both. When the list mixes standards, name the standard of the mating flange.
| Size | JIS 10K | EN 1092-1 PN16 | ASME Class 150 |
|---|---|---|---|
| 25A · DN25 · NPS 1 | 125 / 90 · 4 × 19 | 115 / 85 · 4 × 14 | 108 / 79.4 · 4 × 15.9 |
| 50A · DN50 · NPS 2 | 155 / 120 · 4 × 19 | 165 / 125 · 4 × 18 | 152.4 / 120.7 · 4 × 19 |
| 80A · DN80 · NPS 3 | 185 / 150 · 8 × 19 | 200 / 160 · 8 × 18 | 190.5 / 152.4 · 4 × 19 |
| 100A · DN100 · NPS 4 | 210 / 175 · 8 × 19 | 220 / 180 · 8 × 18 | 228.6 / 190.5 · 8 × 19 |
| 150A · DN150 · NPS 6 | 280 / 240 · 8 × 23 | 285 / 240 · 8 × 22 | 279.4 / 241.3 · 8 × 22.2 |
| 200A · DN200 · NPS 8 | 330 / 290 · 12 × 23 | 340 / 295 · 12 × 22 | 342.9 / 298.5 · 8 × 22.2 |
| 250A · DN250 · NPS 10 | 400 / 355 · 12 × 25 | 405 / 355 · 12 × 26 | 406.4 / 362 · 12 × 25.4 |
| 300A · DN300 · NPS 12 | 445 / 400 · 16 × 25 | 460 / 410 · 12 × 26 | 482.6 / 431.8 · 12 × 25.4 |
Values in millimetres; ASME dimensions converted from inches.
Sources
EN 1092-1 PN6, PN10 and PN16: KVT’s extract of DIN EN 1092-1:2013, checked against SAMSON worksheet AB 02, which also gives PN25 and PN40. JIS 10K: MIE Techno’s JIS B 2220 table published on MISUMI; JIS 5K: Wermac’s table, matching Tsuruga’s; JIS 16K: Wermac’s 20K table (16K and 20K share connection dimensions), with bolt counts and threads checked against Nichias’ 16K bolting table. ASME B16.5 Class 150 and 300: Engineering ToolBox, checked against Project Materials and API International; bolt holes are 1/8 in larger than the bolt. Gaskets: Gore’s EN 1514-1 (type IBC) and ASME B16.21 tables, every outside diameter checked against the flange (bolt circle minus hole for EN, bolt circle minus bolt for ASME). JIS B 2404 gaskets for 5K, 10K and 16K: Nichias’ tables; their outside diameter is also the bolt circle minus the bolt, and the 84 mm inside diameter at 65A is confirmed by Daiko’s 10K gasket.
Before you send the flange
Questions about flanges in an RFQ
Will a JIS 10K flange bolt to a PN16 flange?
Not in general. At DN50 the bolt circles are 120 mm (JIS 10K) and 125 mm (EN PN16), at DN100 175 and 180 mm. Order the flange standard of the mating pipework, and say it in the request.
Is it PN10 or PN16?
Up to DN150 the two have the same drilling, so a measurement cannot tell them apart; from DN200 they differ, for example 8 holes for PN10 and 12 for PN16 at DN200. The rating comes from the flange marking, the valve plate or the drawing.
What is the difference between JIS 10K and 16K?
Up to 40A the drilling is the same. At 50A and 65A a 16K flange has 8 holes where 10K has 4, on the same bolt circle; from 80A the 16K bolt circle and outside diameter are larger.
Which gasket fits the flange?
Each candidate shows the ring gasket that sits inside the bolts, as inside × outside diameter: EN 1514-1 type IBC for EN flanges, an ASME B16.21 flat ring for ASME flanges and a JIS B 2404 gasket for JIS flanges. The drilling does not set the thickness or the material; take those from the old gasket or the system’s specification.
What if nothing matches?
Check the outside diameter, the bolt circle and the hole count again, then send a photograph of the flange with a ruler across it and the figures. BS 10 tables, ASME B16.47 large-diameter flanges and maker-specific flanges are outside this tool. The international shore connection and the MARPOL discharge flanges have a page of their own, and the identifier names them when the figures fit.
Flange identified, photo taken?
Send the measurement with the photograph.
An identified drilling is a cross-check on your measurement, not proof. Attach a photograph of the flange with a ruler across it, give all the figures and the valve plate, and Vessel Core checks them against each other before an offer goes back.
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