Basic diameter - no chart in the register measures this size
The visual tell
What the end of the fitting looks like
Schematic cross-section of the male half, upper side only, with the centre line dashed and the open end on the left. Cone angles are drawn at their true angle from the axis; nothing else is to scale and no dimension should be measured off it. Thread shown: M16 x 1.5.
A shallow internal cone at the bottom of a straight metric port, with a cutting ring or a captive soft seal sitting in it.
Where it seals: The 24 degree cone against a cutting ring bitten into the tube, or against a soft seal captured in the cone on the sealing-cone version.
Dimensions
Thread size, pitch and diameters for 8S (M16 x 1.5).
Designation
8S (M16 x 1.5)
Thread
M16 x 1.5
Threads per inch / pitch
1.5 mm pitch
Basic major diameter (male)
16 mm / 0.63 in
Measured across the male crests
Not published - fewer than two identification charts in the source register carry this size
Basic minor diameter (mating female)
14.38 mm / 0.566 in - computed from the 60 degree thread profile, not measured
Thread form
60 degree flank angle, parallel
Seat
24 degree cone (DIN)
Tube outside diameter
8 mm (0.315 in)
Series
S, heavy (high pressure)
How the size is named
Sized by tube outside diameter in millimetres AND by series: the same thread can carry two different tube sizes depending on whether it is light or heavy series.
M16 x 1.5 carries two different tube sizes: 8 mm in the heavy (S) series and 10 mm in the light (L) series. The thread alone does not tell you which fitting you have - the cutting ring is bored for one tube diameter and will not grip the other.
Working pressure
Published working pressure630 bar (9,137 psi)
This figure applies only under these conditions: Cutting-ring connection in carbon or stainless steel under static working conditions, at a safety factor of 4, per the DIN 2353 / PN-ISO 8434-1 table. The lower figure is the ISO 8434-1 cutting-ring value; the upper is the higher of the two published manufacturer figures for the size. Fittings that seal metal to metal, and banjo fittings, run at a safety factor of only 1.5 to 2.5 and are rated lower. Above 100 degrees C the figure may need reducing.
A fitting with two different ends is only ever as strong as the weaker end, and any rating assumes the fitting is undamaged, correctly assembled and within its temperature range. Pressure ratings are safety-relevant: confirm them against the manufacturer specification before the system is charged.
What it mates with
A M16 x 1.5 straight metric port with a 24 degree internal cone, in the same S series. The cutting ring or soft seal is sized to the 8 mm tube, so the series has to match as well as the thread.
The cutting ring and the tube outside diameter have to match the series. A light-series ring on a heavy-series body, or the wrong tube diameter, will not bite properly and the joint will blow out under pressure.
Do not mix these up
Fittings that measure like a 8S (M16 x 1.5)
Every size below sits within 0.9 mm of this one across the male thread crests, which is inside what a worn or plated fitting and a hurried measurement produce together. Those marked same thread will screw together with this fitting.
Fittings in other standards whose male thread diameter is close to 8S (M16 x 1.5).
No - 0.66 mm apart on diameter, and a different pitch
This list is computed from the published diameters in the database rather than kept as a hand-written list, so a correction to a table can never leave a stale warning behind.
Answers
Common questions about 8S (M16 x 1.5)
What thread is a 8S (M16 x 1.5) fitting?
8S (M16 x 1.5) runs a M16 x 1.5 thread: 1.5 mm pitch, basic major diameter 16 mm / 0.63 in. No two identification charts in the source register measure this size, so no caliper figure is published for it.
How do I tell a 8S (M16 x 1.5) apart from a fitting that measures the same?
Look at the sealing surface. A shallow internal cone at the bottom of a straight metric port, with a cutting ring or a captive soft seal sitting in it. The 24 degree cone against a cutting ring bitten into the tube, or against a soft seal captured in the cone on the sealing-cone version. The thread is parallel (straight) and the flank angle is 60 degrees.
What does a 8S (M16 x 1.5) screw into?
A M16 x 1.5 straight metric port with a 24 degree internal cone, in the same S series. The cutting ring or soft seal is sized to the 8 mm tube, so the series has to match as well as the thread.
What pressure is a 8S (M16 x 1.5) rated for?
630 bar (9,137 psi). Cutting-ring connection in carbon or stainless steel under static working conditions, at a safety factor of 4, per the DIN 2353 / PN-ISO 8434-1 table. The lower figure is the ISO 8434-1 cutting-ring value; the upper is the higher of the two published manufacturer figures for the size. Fittings that seal metal to metal, and banjo fittings, run at a safety factor of only 1.5 to 2.5 and are rated lower. Above 100 degrees C the figure may need reducing.
Dimensions are as defined by ISO 8434-1, DIN 2353. FittingKey is an independent reference and is not affiliated with, endorsed by or approved by any standards body or fitting manufacturer.
Every value on this page was checked against 5 independent published sources:
Four publishers give the same thread-to-tube map for both series, including the eight threads that carry a different tube size in each series.
Basic major diameter
gates-idchart, mcgill-id
The basic major diameter of an ISO metric thread is the number in its designation: M18 x 1.5 measures 18 mm across the crests. Both charts print exactly that.
Working pressure
tubes-int, adaptall-24
One publisher gives the ISO 8434-1 cutting-ring figure together with the spread across producers and states the conditions in full - carbon or stainless steel, static, safety factor 4. The other gives a single figure per size band. Where they differ the page prints both.
Sources disagree: DIN 2353 heavy series, 30 mm tube, working pressure.
400 bar (adaptall-24)
250 bar as the ISO 8434-1 cutting-ring figure, 250 to 315 bar across producers (tubes-int)
The 400 bar figure sits outside the producer range the other source publishes for the same size band, which is the only place in the metric table where that happens. Both figures are printed on the size page. Assume the lower one unless the fitting's own catalogue says otherwise.