Thermometer scale magnifier

A magnifying indicator for a thermometer or similar columnar instrument, said indicator consisting of a one-piece body of transparent plastic formed with a cylindrical base block and an upstanding lens on the front portion of the base block. Opposite the lens the base block is formed with a rearwardly-facing vertical V-groove in which the columnar instrument is receivable. A U-shaped wire spring is anchored at one side of the groove and transversely overlies the groove. The spring is arranged to allow the columnar instrument to be slipped into the groove so as to engage against the flat sides thereof and thereafter to clamp the instrument in the groove to prevent angular disorientation of the lens relative to the columnar instrument, while permitting sliding adjustment of the magnifying indicator along the instrument scale.