A Winkle groober was a tool. Rodan asked the Fourth Doctor to hand her one when modifying the TARDIS control console to repair Gallifrey's quantum force field. (TV: The Invasion of Time)
Behind the scenes
The spelling of this oddly-named item has been subject to some contention. Rodan and the Doctor pronounce it "vinkle groober", and DWM 582's The Fact of Fiction on The Invasion of Time parts five and six explains that it was scripted as "Winkle groober". Meanwhile, the captions for the episode call it a "finkle groober", and the Target novelisation Doctor Who and the Invasion of Time merely states that "Rodan muttered something that sounded like 'inkle grooner'." Alien Bodies also makes mention of a Winklegruber neural parameter predictor.