I'm using a Pro-Ject Phono Box MKII phone preamp with an M-Audio2496
sound card to copy vinyl to CD.
The output level of the MKII is too high for the sound card input and
the card clips.
Is there a commercially available line level pad of, say 5 - 10 dB,
that I could use between the two devices?
Can you tell me how to build a pad?
An adjustable pad would be great if it exists. (I didn't have this
problem when I was using my McIntosh preamp since I could adjust the
output level.)

Specs:

Pro-Ject MKII
Input impedance 47k ohms
Output voltage 300 mV @ 1kHz
Max. output 9.5 V (1kHz)

M-Audio 2496
Peak Analog Input Signal +2dBV
Input Impedance 10k ohms minimum

dh wrote ...
Is there a commercially available line level pad of, say
5 - 10 dB, that I could use between the two devices?
Can you tell me how to build a pad?
An adjustable pad would be great if it exists.

A simple stereo "volume control", $5 from Radio Shack
is "an adjustable pad" for your purposes.

(I didn't have this problem when I was using my McIntosh
preamp since I could adjust the output level.)

Your McIntosh used a "volume control" ("potentiometer")
as an "adjustable pad".