For mounting bracket using M6x1.0 fasteners in steel with precise tolerances, what clearance hole size would you specify?

• A. 6.60 mm (G)
• B. 6.30 mm (E)
• C. 6.50 mm (F)
• D. 6.20 mm (C)

Answer: (B)

The test is about choosing a clearance hole size that allows a through-bolt to pass while keeping tight control over fit in a high-tolerance assembly. For an M6 bolt, the nominal diameter is 6.0 mm, so you need a hole larger than 6.0 but not so large that you lose alignment or stiffness. With precise tolerances, the aim is the smallest hole that still clears the bolt, to minimize play while tolerating burrs and misalignment. A 6.30 mm hole provides about 0.30 mm of clearance, which is enough for easy insertion without introducing excess looseness. A smaller hole like 6.20 mm risks interference due to manufacturing variation, burrs, or misalignment. Larger options such as 6.50 or 6.60 mm would introduce unnecessary looseness and degrade positional accuracy. So, 6.30 mm is the best choice because it strikes the right balance between clearance and precision.