Files — grade identification by teeth count If a file has 20 teeth within a length of 25 mm (approximately 20 teeth per inch), what is this file commonly called with respect to its cut grade?

Introduction / Context:Files are graded by coarseness based on the number of teeth per unit length. Coarser files remove material faster but leave a rougher finish; finer files provide better surface finish with slower stock removal. Recognising the grade from a tooth count helps in correct tool selection.

Given Data / Assumptions:

• Teeth count is 20 within 25 mm (≈ 20 TPI).
• Classification follows common workshop practice where fewer teeth per inch indicate a coarser (rough) cut.
• Single-cut or double-cut details do not alter the grade naming here.

Concept / Approach:As the number of teeth per inch increases, the file becomes finer. Typical qualitative order (from coarse to fine) is: rough > bastard > second cut > smooth > dead-smooth. Around 20 teeth per inch falls in the coarse range, corresponding to a “rough” file in many workshop charts. By contrast, smooth and dead-smooth files would exhibit significantly higher tooth densities.

Step-by-Step Solution:Interpret the given count: 20 teeth in 25 mm ≈ 20 TPI.Compare to qualitative ranges: low TPI = coarse.Select the matching grade: “rough file”.

Verification / Alternative check:Reference tables in fitting textbooks show rough files with the lowest tooth densities, often near this value, with successive grades having increasing TPI.

Why Other Options Are Wrong:

• Bastard / Second cut: intermediate tooth densities, finer than rough.
• Smooth / Dead-smooth: substantially higher tooth counts for finishing.

Common Pitfalls:Confusing TPI with teeth per centimetre; ensure consistent units when comparing to charts.

Final Answer:rough file