Wheel spinners, also called knock-ons or knock-offs, are the central securing fitting for centre-lock wheels. On the MGA, spinners are used for two distinct wheel types: the Dunlop 48-spoke wire wheel fitted as optional equipment to pushrod cars, and the Dunlop centre-lock disc wheel fitted as standard to Twin Cam and De Luxe cars. The spinner type fitted to a particular car depends on the wheel type, the variant, the chassis number and the original market of supply. Spinners are handed, left-hand thread on the right-hand side of the car, right-hand thread on the left-hand side, so that wheel rotation under normal driving tightens rather than loosens the spinner.
Pushrod Wire Wheel Spinners, Eared Knock-Ons
The standard spinner for pushrod MGAs with optional wire wheels is the two- or three-eared knock-on. Three distinct patterns were used during the MGA pushrod production run, and all three were fitted to the Dunlop 48-spoke 4J x 15 wire wheel. The earliest pattern carried the MG badge at the centre of the knock-on, with the words "right (off) side" or "left (near) side" moulded into the casting and the word "undo" accompanied by a directional arrow indicating the correct hammer direction for release. From car/chassis 40857, the knock-on was modified to a more curved section across the centre, an appearance change rather than a functional one, with the MG badge retained.
From car/chassis 48730, the MG badge was deleted from the knock-on centre, giving a third pattern that was used through to the end of the 1500 production run and carried over to the 1600 and 1600 Mk II where wire wheels were specified. When ordering a pattern-correct knock-on for a specific pushrod MGA, the chassis number must be confirmed against these two breakpoints, a badged knock-on is not correct for a late 1500 or any 1600-series car, and the later curved-centre pattern is not correct for very early 1500 cars.
Pushrod Wire Wheel Spinners, Octagonal Spinners
From October 1958, at approximately 1500 car/chassis 57500, octagonal spinners were introduced on cars for the German market and subsequently also for the Swiss market. The octagonal spinner is a hexagonal-in-cross-section fitting rather than an eared knock-on, and is tightened or released using a dedicated octagonal spanner rather than a copper hammer. Octagonal spinners never carried the MG badge. The change was initially market-specific, the octagonal pattern was introduced in response to regulations that prohibited projecting knock-on ears considered a hazard to pedestrians or cyclists.
Export cars with octagonal spinners were supplied from the factory with a special octagonal spanner as part of the toolkit.
Twin Cam and De Luxe Knock-Ons
The Twin Cam and De Luxe use a completely different centre-lock system, the Dunlop peg-drive disc wheel rather than the splined-hub wire wheel, and the knock-on for these cars is not interchangeable with any pushrod wire wheel knock-on. The Twin Cam knock-on has a coarser thread than the pushrod item, matching the Twin Cam's different centre-lock hub. The knock-on itself was modified at Twin Cam car/chassis 1826 (April 1959), with the material changing from steel to bronze. Bronze knock-ons were less prone to thread damage and damage from copper-hammer blows than the earlier steel items.
Twin Cams supplied to the German market were fitted with octagonal spinners from Twin Cam car/chassis 708 (October 1958) rather than the standard eared knock-on, an introduction that predates the pushrod market change by approximately six months. The bronze knock-on and, for German-market cars, the octagonal spinner pattern were carried over unchanged on the De Luxe variants.
Thread Direction and Handedness
All MGA knock-ons and spinners, pushrod wire wheel and Twin Cam / De Luxe alike, are handed so that wheel rotation under normal driving tightens the fitting rather than loosens it. The right-hand side of the car uses left-hand thread spinners; the left-hand side uses right-hand thread spinners. The spinners are clearly marked from the factory with either the word "right (off) side" or "left (near) side" and an "undo" arrow indicating release direction, or equivalent identification on later patterns. Fitting a spinner to the wrong side of the car, even if the thread engages, is dangerous: driving will progressively loosen the spinner rather than tighten it, and the wheel may detach.
Fitting and Removal
Wheel spinners are installed and removed using a copper or hide-faced hammer (covered under the Wheel Nuts, Caps, Clamps & Tools node, Node 907) or, for octagonal spinners, using the special octagonal spanner supplied with export cars of the period.