If you look at the wheel between the lug nuts you will see various numbers, letters, and logos cast into the metal.

One sequence will resemble - 6.5Jx15H2 (one of my '95 855 wheels)

The 6.5 is the rim width in inches,

As for the J and the H2 -

One is the bolt circle size, and the other is the offset, which is a measure of how far the mounting flange that contacts the brake rotor is from the center of the tire.

the 15 is the wheel diameter.

The offset is quite important and although you could use several wheels on your car, you should find a wheel that matches the measurement numbers of your other wheels exactly


An addition - I see a steel wheel in my collection marked 15Jx15x43

The J is the bolt circle size, and the 43 is the offset
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 435,000 miles put on 9 bricks