Specification summary of ASME B18.6.3 as applied to oval-head machine screws: the dimensions the standard controls, the full specified size range, and the equivalent DIN/ISO/ASME designations.
ASME B18.6.3 — Scope
ASME B18.6.3 is "Machine screws and machine screw nuts (inch series)". An inch-series document; sizes are numbered gauges and fractional inches, not metric.
Material, property class, surface finish and packaging are governed by separate documents — ISO 898-1 and ISO 898-2 for mechanical property classes, ISO 4042 for electroplated finishes.
Tolerance & Product Grades
ASME B18.6.3 does not divide oval-head machine screws into product grades. Tolerances are given as limits on the individual dimensions in the table.
Where a general-tolerance class is cited on the drawing instead, it applies to the dimensions not otherwise toleranced.
Dimensions Specified by ASME B18.6.3
| Size example | Length (in) | Drive | Head form | Material options | Reference standard |
|---|
| #8-32 | 2 | Phillips | oval raised countersunk | 18-8 stainless steel / steel | ASME B18.6.3 |
| inch machine-screw sizes | | Phillips | oval raised countersunk | 18-8 stainless steel / steel | ASME B18.6.3 |
Equivalent Standards
Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Oval-Head Machine Screws page.
Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry.
When to Specify ASME B18.6.3
ASME B18.6.3 is the inch-based reference; for metric programs choose the ISO equivalent instead.
Custom manufacturing · Made to drawing
Need a screw to this standard in a non-standard size?
Parts built to ASME B18 6 3 are already in the catalog, so a special is usually a variation on existing tooling rather than a new design — which is what keeps the cost down. Made by cold heading or warm forging.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
Custom screw manufacturingSend a drawing
Applications & Industries
Oval-Head Machine Screws are bought for a small number of well-defined jobs. These are the ones we ship them for. Stocked from #8-32 to inch machine-screw sizes (nominal diameter).
Industries that specify Oval-Head Machine Screws
-
Light fabrication
ASME B18.6.3 sizes fit inch machine-screw joints.
-
Visible equipment
Oval heads provide a finished raised profile on covers and trim.
-
Instrument panels
Phillips drive supports routine assembly in a low-profile raised seat.
-
Appliance housings
Stainless and steel options match the enclosure material.
-
Energy & infrastructure
Tower, pipework, switchgear and plant fixings specified for long service life and inspectable joints.
-
Maintenance & MRO
Stocked replacements matched to an existing property class, thread and finish.
Typical applications
- selecting steel or 18-8 stainless
- seating a raised oval head on a prepared countersink
- choosing the under-head length for the panel stack
- using a Phillips driver on a visible machine screw
- joints where the property class is stated on the drawing
- clamping two machined faces to a calculated preload
Service conditions to specify against
- Marine and coastal
- Available in A4 (316) stainless for chloride exposure — coastal structures, pool halls, water treatment and deck hardware, where A2 will eventually pit.
- High load
- Supplied in ISO 898-1 property classes, so the joint can be designed to a stated proof load and tightened to a calculated torque rather than by feel.
- Torque and preload
- The joint is designed around bolt tension, so lubrication, coating and the friction coefficient all change the torque figure — state them together.
Where to use something else
- Do not use an oval head in a flat-bottom counterbore; the raised profile needs its matching seat.
- Do not use a machine thread into unthreaded sheet or timber; use a tapping screw, rivet nut or insert made for that parent material.
Full application guide: where Oval-Head Machine Screws are used, how to specify them, and the cases they are wrong for
