What are volumetric pipettes primarily used for?

Volumetric pipettes are specifically designed for precise volume measurements in laboratory settings. They have a bulbous center and a single calibration mark, making them ideal for delivering an exact volume of liquid, usually in the range of 1 mL to 250 mL. This precision is essential when preparing reagents, measuring standards, or creating dilutions, where accurate and repeatable measurements are critical for the reliability of experimental results.

In contrast, the other choices do not align with the primary function of volumetric pipettes. Visual inspection does not require precise volume measurements, while collecting blood samples would typically involve different instruments designed specifically for that purpose, like phlebotomy devices. Cleaning laboratory equipment is unrelated to the measurement and transfer functions that volumetric pipettes provide. Thus, their primary use remains focused on application involving the accurate measurement of liquid volumes necessary in laboratory work.