Which type of hammers are not permitted during straightening?

Ball-peen hammers are not permitted during straightening because of their specific design features and intended use. They have a rounded end that is primarily used for shaping metal, making them ideal for tasks like peening and striking metal to improve its properties. However, when it comes to straightening, a more controlled and flat impact is typically needed to avoid introducing further stress or damaging the material being straightened.

In contrast, other types of hammers, such as claw hammers, sledge hammers, and pneumatic hammers, can serve different purposes that may be more suitable for the process of straightening. Claw hammers can provide a flatter striking surface that is more appropriate for general use. Sledge hammers can deliver more force when needed for significant adjustments, while pneumatic hammers can offer controlled force and efficiency in straightening operations.

Thus, the specific design and intended function of ball-peen hammers make them unsuitable for straightening activities.