Mounting Flange/Boss: Pilot Diameter Tolerance H7/g6 fit

Component Specifications

Definition

A mounting flange or boss is a machined component integral to port bodies and fittings, engineered to facilitate the secure and precise connection of adjacent machine elements. It typically consists of a flat, circular, or rectangular projection with drilled and tapped holes for bolts, ensuring proper alignment, load distribution, and sealing integrity in fluid or mechanical systems. The design incorporates features like pilot diameters, dowel pin holes, or O-ring grooves to maintain positional accuracy and prevent leakage under operational stresses.

Working Principle

The mounting flange/boss operates on the principle of providing a rigid, precisely located interface for bolted connections. It transfers loads (such as mechanical forces, vibrations, or pressure) from the attached component to the main port body, distributing stress evenly through its geometry and fastener pattern. Alignment features ensure correct orientation, while sealing surfaces prevent fluid or gas leakage, maintaining system integrity.

Materials

Common materials include carbon steel (e.g., AISI 1045), stainless steel (e.g., AISI 304 or 316 for corrosion resistance), aluminum alloys (e.g., 6061-T6 for lightweight applications), or ductile iron. Material selection depends on factors like strength requirements, corrosion resistance, weight, and cost. Specifications often include hardness (e.g., Rockwell C scale for steel), tensile strength, and surface finish (e.g., Ra 1.6 μm for sealing surfaces).

Technical Parameters

Parameter	Typical range	Notes & selection driver
Bolt Size	M6 to M16 metric or equivalent imperial
Pressure Rating	Up to 300 bar (depending on design)
Flange Thickness	10 mm to 30 mm
Surface Flatness	0.05 mm per 100 mm
Bolt Circle Diameter	Varies by application (e.g., 50 mm to 200 mm)
Number Of Bolt Holes	Typically 4, 6, or 8
Pilot Diameter Tolerance	H7/g6 fit

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 6162, ISO 3019-2, DIN 2501, SAE J518

Parent Products

This component is used in the following industrial products

Port Body / Fitting

The main structural component of a pressure test port that provides the connection interface and housing for internal elements.

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Engineering Analysis

Risks & Mitigation

Misalignment during assembly
Bolt over-torquing
Corrosion in harsh environments
Fatigue cracking under cyclic loads
Leakage due to poor surface finish

FMEA Triads

Trigger: Improper bolt torque during installation
Failure: Stripped threads or cracked flange, leading to connection failure and potential system leakage
Mitigation: Use calibrated torque wrenches, follow manufacturer specifications, and implement training for assembly personnel

Trigger: Material corrosion in wet or chemical environments
Failure: Reduced structural integrity, leading to cracks or bolt hole enlargement and eventual component failure
Mitigation: Select corrosion-resistant materials (e.g., stainless steel), apply protective coatings, and conduct regular inspections

Trigger: Vibration or cyclic loading in operation
Failure: Fatigue cracking at stress concentration points (e.g., bolt holes), resulting in catastrophic failure over time
Mitigation: Design with adequate fillet radii, use fatigue-resistant materials, and implement preventive maintenance schedules

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Geometric tolerances per ISO 1101 (e.g., flatness within 0.1 mm, position tolerance for bolt holes within 0.05 mm). Dimensional tolerances for critical features like pilot diameters typically follow ISO 286 (e.g., H7 for holes, g6 for shafts).

Test Method

Testing includes dimensional inspection using CMM (Coordinate Measuring Machine) or gauges, pressure testing to verify sealing integrity (e.g., hydrostatic test per ISO 5208), and material certification (e.g., mill test reports for metals). Non-destructive testing (NDT) like dye penetrant or ultrasonic inspection may be used for crack detection.

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

Check the legal entity, factory address, ownership, certifications, and direct contacts.

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Manufacturers of Mounting Flange/Boss

Manufacturer profiles associated with Mounting Flange/Boss.

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

What is the difference between a mounting flange and a boss?

A mounting flange is typically a flat, extended surface with bolt holes for connecting larger components, while a boss is a smaller, raised projection often used for localized attachment or reinforcement. In practice, the terms are sometimes used interchangeably for port body fittings.

How do I select the right material for a mounting flange/boss?

Consider operational environment (e.g., corrosion, temperature), load requirements, weight constraints, and compatibility with connected parts. For example, use stainless steel in corrosive settings, aluminum for lightweight needs, or carbon steel for high-strength applications.

What are common failure modes for mounting flanges/bosses?

Common failures include bolt hole stripping due to overtightening, cracking from fatigue or impact loads, misalignment causing leakage, and corrosion leading to structural weakness. Proper installation, material selection, and regular inspection can mitigate these risks.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Mounting Flange/Boss