Our wheels are designed with 16mm diameter lug stud / bolt holes, and generally, unless custom ordered otherwise, are specified to use a 60 degree conical seat lug type. Many, if not most, of our wheels are also specified to use a small diameter, splined lug nut / bolt type. 'Splined' simply means that an additional tool that slides over the outside of the nut / bolt instead of a traditional socket is used to install and remove the lug nuts / bolts.
Some of our wheels are specified to use a different, ball-type seat lug bolt. This style of fastener is common to some European vehicle makes as an OEM specification.
A visual and tactile inspection of the seat area of the wheel should suffice to determine if the wheel is conical seat or ball seat type.
Ball seat wheels will have a curved surface for the lug nut to seat onto, while conical seat wheels will have a straight, conical area.
To ensure a proper fit and maintain the wheel warranty we recommend using Gorilla Automotive small diameter splined lugs. The conical taper is matched to our conical seat wheel designs and the thin-walled socket works well with most wheel designs. You can find Gorilla Automotive products via your favorite online retailer or at most local wheel & tire shops.
Older, vintage wheels used a mag lug with washer...if your lug hole appears flat with no taper please visit your local dealer to identify and purchase the proper lug nuts for your wheels.
http://www.gorilla-auto.com/
http://www.wheelpros.com/dealers