4024. It looks the same, except that six screws hold the horn tweeter/mid/high frequency adjustment panel, rather than ten, as in the 4024. The 4024s fifteen inch woofer had a lifetime rubber surround, where the 4029 has a foam surround that rots. I just finished refoaming the woofers. This is my third pair of Mach Ones, but my first 4029s. The woofers were easy to refoam, but slow. They speakers sound better than I remember, are awesome for dance and reggae, and I think the 4029 has even better bass than the 4024.
Horn loaded speakers aren't usually my thing, but it's easy to see what the fuss was about.