The recommended depth for drilling holes to insert cemented pins is 3-4 mm because this depth provides adequate anchorage in the bone to ensure pin stability without compromising bone integrity. Drilling too shallow (< 3 mm) risks insufficient mechanical retention, while excessive depth (> 4 mm) increases the risk of bone weakening and microfractures. Maintaining the correct depth optimizes the strength of the fixation and minimizes complications related to pin loosening or fracture propagation. Therefore, 3-4 mm balances pin retention strength and bone preservation effectively.

Reference: Campbell's Operative Orthopaedics, 13th Edition.