Riveted and welded joints — thickness range suited to lap joints In fabrication practice, lap joints are generally preferred for relatively thin plates. For which thickness range are lap joints typically employed?

Introduction / Context:
Joints in sheet and plate fabrication are selected based on thickness, load path, ease of assembly, and inspection requirements. Lap joints overlap members and are common in thin-gauge work for both riveting and welding (especially resistance spot welding).

Given Data / Assumptions:

• General fabrication context (sheet-metal, light structures).
• Focus on practical workshop guidance rather than a strict code clause.
• Thinner plates permit easy overlap without excessive step height.

Concept / Approach:
Lap joints avoid the need for edge preparation and maintain alignment easily on thin sheets. As thickness increases, the offset created by the overlap becomes less acceptable, stress contours worsen, and butt joints with proper edge preparation are preferred. For very thin sheets (below roughly 3 mm), lap joints are convenient and economical.

Step-by-Step Solution:
Relate joint type to plate thickness.Recognise that thin sheets favour lap joints for ease and speed.Select “less than 3 mm”.

Verification / Alternative check:
Shop standards for sheet-metal ducts, enclosures, and automotive body panels overwhelmingly use lap configurations in these thin thicknesses.

Why Other Options Are Wrong:

• 5 to 10 mm / 12.5 mm / above 25 mm: butt joints with full penetration or multi-pass welds are typically specified; lap joints become bulky and create stress raisers.
• Exactly 20 mm: not representative of common lap-joint usage.

Common Pitfalls:
Confusing riveted boiler joints (historical) with modern sheet-metal practice; the typical classroom guideline emphasises lap joints for thin plates.

Final Answer:
less than 3 mm