Steering boss guide

“Your guide to choose the right steering boss for your car“

Find your PCD (Pitch Circle Diameter)

The pitch circle diameter (PCD) can be found by measuring from the middle of one fixing hole to the middle of another fixing hole on the opposite side (across the centre hole) on the pitch circle diameter of the fixing ring of screws.

PCD’s of commonly used steering wheels

6 bolts x 74mm (one bolt facing north)
– Nardi
– Luisi
– Raid
– Personal
– Mountney ‘M’ range
bolts used: 5.5mm

6 bolts x 70mm
– Sparco
– OMP
– MOMO
– NRG
– Sabelt
bolts used: 5.5mm

9 bolts x 101.6mm (4″)
– Mountney traditional
– Moto-lita
bolts used: 5.5mm

Mini Classic (and Innocenti) PCD values and what boss to fit

All mini classics up to 1996 (MPi) used a different variant of the same steering column, at least the diameter of 3/4″ (19mm), and splines (48 splines) stayed the same! therefore we only have to talk about the upper PCD of the different steering wheels and bosses (MPi Mini’s excepted). Innocenti used their own steering bosses and is therefore named separately in this list.

Mini steering bosses (Austin, Morris, Rover, BL)
– PCD of 6x70mm or 6x74mm
1959 to 1996 mountney ‘M’ range steering boss in black; KK154X

– PCD of 9×101.6mm (4″)
1959 to 1996 mountney classic range steering bosses in black or chrome; MB008 / MB008C

– PCD of 9×101.6mm (4″) with classic style push button horn
1959 to 1996 Moto-lita original wheel boss for push button B1OE
this boss (B1 OE) is special made in order to receive the push button horn from the classic Mini’s off back in the day, how that looks? look here:

As said before, this B1OE has a PCD of 9×101.6mm (4″) and therefore can be used with both the original Mota-lita steering wheels and with the Mountney (not ‘M’) steering wheels. Other steering wheels are also widely available in this size and therefore could be retrofitted with these push-button horn assemblies of back in the day
– Morris horn; 27H6944
– Austin horn; 27H6943

These horns can only be mounted on the original Bakelite Mk1 steering wheel, with the small hole in the bottom to screw the horn-push into place, or the aftermarket boss from Moto Lita (B1OE), commonly known as the ‘tulip’ boss. Brooks Motors however, is developing their own boss that is much cheaper and will make your Morris badge (71.8mm) fit and has the PCD of 101.6mm. On the upside, this boss fits both 6 and 9 bolt configurations. (6×101.6mm and 9×101.6mm)

Innocenti steering bosses
– PCD of 6x70mm or 6x74mm
1967 to 1976 Innocenti Mini Minor boss; BG8308 QSN3201

While the Innocenti Mini has always kept the push button horn in the center they had to make their own boss. MOMO nowadays has a whole array of bosses available for Innocenti with the one above that will fit your Innocenti Mini Classic for sure and let you keep the push button availability.

As their are no bosses with a PCD of 9×101.6mm (4″) listed for sale for Innocenti we offer the availability to use a B-G (MOMO) steering wheel adapter to convert the PCD from 70 or 74mm to this 9×101.6mm.

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Additional information:

Steering wheel bosses

if you want to look up which steering bosses Mountney has available for your car, have a look here, they make the 6 and 9-hole configurations in one and have the right splines for you. https://www.mountneyltd.com/Catalogue/Boss-Kit-Vehicle-Look-Up

B-G/ MOMO steering wheel adaptors

https://www.gprdirect.com/b-g-racing-wheel-adaptor-momo-nardi-to-mountney-moto-lita

Pre-drilled with a 6x70mm & 6x74mm PCD bolt pattern on the inner lip, and 6x101mm & 9×101.6mm PCD bolt patterns on the outer lip, this ingenious adaptor will allow users to fit classic Mountney or Moto-Lita steering wheels with the larger 6x101mm and 9×101.6mm PCD to a Momo hub kit or any other hub kit with a 6×70 or 6x74mm bolt pattern.

The elegant, compact design will bring the steering wheel just 10mm closer to the driver, and allows for a centre ring and horn button to fit neatly and securely providing a tidy flush finish. The perfect companion for those wanting to utilise a classic steering wheel with a modern hub.

B-G Steering Wheel Adaptors are produced from high quality aluminium with an elegant black anodised finish and laser etched B-G logo, and are simple to fit using the fixing screws provided.

Extra information from Moto-lita

Our standard steering wheels have 9 equally spaced fixing holes (5.5mm) on a PCD of 101.6mm (4″).

Our small centre MK3 & MK4 wheels(to fit a B20 S/C boss only) have a PCD of 79.40mm.
E-type OEM wheels have a PCD of 77.8mm (12 o’clock to 6 o’clock).
AC Cobra wheels have a PCD of 62mm on the diagonal slant (1 o’clock to 7 o’clock).
Aston Martin wheels have 9 fixing holes (5.2mm) on a PCD of 68.26mm
Jaguar D-Type wheels have 9 fixing holes on a PCD of 68.58mm.
GT40 wheels have 6 fixing holes (6.1mm) on a PCD 78mm. 
Momo drillings have 6 fixing holes on a PCD of 70mm.
Nardi drillings have 6 fixing holes on a PCD of 74mm.