25-09-2026

Flange Size Chart: Dimensions and Weights for Weld Neck, Slip-On, Blind, Socket Weld, Lap Joint and Threaded Flanges

Six flange types cover almost every piping job: Weld Neck, Slip-On, Blind, Socket Weld, Lap Joint and Threaded. This guide ties each one to ASME B16.5, ASME B16.47 and EN 1092-1, with the dimensions for three tasks:

• Quotation: OD and unit weight, for freight and handling
• Fabrication: thickness, bore and facing
• Installation: bolt circle, hole count and hole size

Quick comparison

A matching DN or NPS does not guarantee a matching bolt pattern. Same size, different standard, different series or different pressure class can all mean different drilling. Always check the bolt circle, hole count and hole diameter separately from the nominal size. That single check causes more fit-up failures than any other on this list.

Which standard, and when

ASME uses imperial bolting (⅝”, ¾”…); EN 1092-1 uses metric (M16, M20…). Series A and Series B under ASME B16.47 use different bolt circles and hole counts at the same size, too, so state which series on every large-diameter order.

Common size cross-references for buying across systems: NPS 2″ = DN 50, NPS 4″ = DN 100, NPS 6″ = DN 150, NPS 12″ = DN 300.

The six types, briefly

• Weld Neck (WN / EN Type 11) — built for higher-pressure, cyclic service. The bore has to match the exact pipe schedule; that match is the most common fit-up error on this type. The long-welding-neck variant is EN Type 21.
• Slip-On (SO / EN Type 01/12) — the bore is sized slightly larger than the pipe OD so the pipe seats before the two fillet welds go on. Easier alignment, lower pressure service.
• Blind (BL / EN Type 05) — no bore, so drilling and thickness carry the fit-up check. Consistently the heaviest of the six types at a given size — factor that into lift planning early, not on delivery day.
• Socket Weld (SW / EN Type 14) — small-bore, high-pressure lines. The socket bore is the fit-up check: the pipe has to seat cleanly before fillet welding.
• Lap Joint (LJ / EN Type 02/04) — a loose flange over a welded stub end, used where frequent dismantling is expected. Check the flange bore against the stub-end OD, not the pipe OD. Total weight = flange + stub end, and the two parts often ship in different material grades, so specify and quote both together.
• Threaded (THR / EN Type 13) — no welding, so the thread has to be right the first time. A mismatched thread form is a leak, not a rework. Specify NPT (ASME) or BSP (EN) explicitly.

Weight pattern by type, same DN and rating

This is a relative guide for rough handling and freight planning only — not a substitute for confirming the exact EN type and PN (or ASME class and series) against the drawing.

What we need from you to specify the right flange

In most projects, the flange isn’t selected freehand — the buyer is working from an end customer’s line spec or drawing. That’s normal, and it’s exactly why getting a few details right at the start matters more than picking a size off a chart. To quote, fabricate and deliver the correct flange, we need:

• Standard: EN 1092-1 or ASME B16.5/B16.47 (and Series A or B, if ASME and above 24″)
• Nominal size: DN or NPS
• Pressure rating: PN or Class
• Flange type: Weld Neck, Slip-On, Blind, Socket Weld, Lap Joint, or Threaded
• Material grade: with Werkstoff number and ASTM grade cross-referenced (e.g. 1.4404 / F316L) so procurement, fabrication and QC are reading the same spec
• Facing / sealing type: raised face, flat face, or ring-type joint

If any of this is missing or unclear on the drawing you’ve received from the end customer, send us what you have — the tie-in point, the connecting pipe spec, or the mill certificate — and we’ll help you confirm the rest before it goes to fabrication.

Belgian and EU notes

For EU projects, lead with DN and PN, not NPS and Class. Decimals use commas and thousands use dots: 12,5 kg, 1.250,50 €. Bolting is metric (M16, M20), which is not interchangeable with ASME’s imperial bolt sizes even at a matched nominal size.

On the purchase order, state EN 1092-1 type, DN, PN and material grade on the same line, for example “Type 11, DN150, PN16, 1.4404”. Cross-reference the Werkstoff number against the ASTM grade on the drawing and mill certificate (1.4404 / F316L is the common pairing) so procurement, fabrication and QC are reading the same spec.

FAQ

How do I choose between ASME and EN flange standards?

Match the standard already used in the connecting system: that decides the bolt pattern, not the nominal size. New-build projects in Belgium and the EU typically specify EN 1092-1 with DN/PN; projects tied to US or Asian supply chains typically specify ASME B16.5/B16.47 with NPS/Class. Mixing the two in one tie-in point means machining a spool piece or using a transition flange, not forcing the bolt pattern to match.

Why can two flanges of the same nominal size fail to match?

Because “same size” only means the bore is close. It says nothing about the bolt pattern. ASME, EN, DIN and ISO don’t share pressure classes, drilling or dimensions, so a DN150 EN flange and an NPS 6″ ASME flange are not interchangeable even though DN150 = NPS 6″ on paper. It also happens within one standard: ASME B16.47 Series A and Series B use different bolt circles and hole counts at the same size. Custom or non-standard flanges add a third way to get caught out.

Which flange type is lightest for a given size?

At the same DN/NPS and pressure rating, socket weld, threaded and slip-on flanges are consistently lighter than weld neck, lap joint or blind flanges, because they carry no hub (or a short one) and no solid disc. Blind flanges are the heaviest by a clear margin, since the entire flange face is solid metal. The right pick still depends on the service: pressure class, weld access and dismantling frequency matter more than weight alone.