|The MGA With An Attitude
SWITCH KNOBS And BEZEL NUTS, MGA - DT-109
For the MGA the switch knobs are small black phenolic knobs with white lettering, very unpretentious, matching the black and white face of the instruments. The switch bezel nuts are chrome plated thin round nuts with flat face and slots in the face for wrenching, in keeping with the general styling and intended impression of a light weight sport racing car. Bezel nuts with chamfered outer edge or wrench slots in the outer edge would be incorrect. The hex nut shown on my ignition switch (red panel) is incorrect, as this should be a thin round nut with slotted (beige panel) face to match style of the smaller nuts. The bezel nut on the turn signal switch is wider with knurled outer diameter to be tightened with your fingers, as the switch housing is phenolic which could be broken if the nut was tightened with a wrench. The thin chrome trim ring on the turn signal pilot light is off center as shown, because the original colored lens (jewel) had a 9-mm thread where recent replacement parts have 8-mm thread (but the chrome ring was not changed to match). The Start and Choke controls have smooth bezels with a hex nut behind the panel.
Left side of dash (Left hand drive) Turn signal, Panel, Fog and Lighting switches
Right side of dash (Left hand drive) Ignition, Wiper and Map switches
Start, Choke, Heater Control and Screen Washer knobs
There was a variation of color for the Screen Washer knob. For a black car with red interior and red painted dash, the optional Screen Washer knob could have red and white decoration as show at far right. Since the screen washer was often a dealer installed accessory, exact location of the manual pump on the dash could vary, and the red trimmed knob could have found its way into different cars. There were various colors and designs of knobs for different aftermarket screenwasher pumps, some of which may be period correct as accessory parts. See Screenwasher in the Accessories section for more details.
On November 26, 2012, Neil McGurk in Cumbria, UK wrote:
"There are three sizes of the switch rings. The smallest is for the "F", wiper and map lamp switches with slightly larger one for the lights and slightly larger still for the panel lamp switch. The heater control knobs have a similar size to the panel lamp, but a finer thread I think. The choke and starter push through from the front and are secured by a nut from behind, but the hole needs to be the correct size and "D" shaped in order for the choke outer cable not to twist in use. The (Tudor and Wingard) washer pumps usually have the same thread as the light switch I believe and can be fitted directly to the dashboard with a light switch trim ring, but the correct period way was to recess the plunger into the dash using a two cups the outer visible one being chromed".
This got my curiosity up, so I spent some time to R&R switch nuts on my car for measurements. I find the smaller thread for Fog, Wiper and Map lights, to be 3/8-24-UNF with 3/4-inch diameter panel nut. Thread on the Lighting switch seems to be 7/16-24-UNF with 7/8-inch diameter panel nut (with incorrect beveled edges in my case). Thread for the Panel light switch and Heater control pull cables seems to be 9/16-32-UN with 3/4-inch diameter panel nut. My thread pitch gauges work fairly well, but the 9/16 threads are not standard bolt sizes, so I don't have a standard nut for comparison. The ignition switch has 3/4-32-UN threads. Mine has the incorrect 15/16" hex nut, while the correct panel nut may be 15/16" or 1" diameter (obviously narrow). The turn signal switch has a more odd thread about 0.720-inch major diameter, and I don't have a clue what thread standard that may be (but I suspect some pre war hold-over design). The accessory screenwasher pump (at least the most common Tudor part) has a 3/8-xx thread that is slightly different pitch from the smaller switches (not 3/8-24-UNF). The smaller switch panel nut will bind after a couple of turns on the washer pump, but it could be used in a pinch if you force it.