I think it would depend on the mast base and step plate you have. I hear more than one model was used in the production. My mast base and step on my 272 are like this:
The photo of the step plate does not show it well, but the aft end of the step plate has a groove cut into each side of the slot. The little tang that drops down on the aft end of the mast base plate has a pin that passes through it. The left and right ends of the pin slide into the slots. Only a few millimeters of the ends sit in the slots. You lay the mast toward the aft of the boat, line up the pin in the slot, and slide the mast base forward into the slot. Then you stand the mast, and the pin stays in the slot.
Most of these pins and / or slots get torn up over the years. Frankly, it is too weak to keep the mast base in the plate or even help keep the mast steady if you get any twist as you erect it or lower it. I replaced the pin on mine when I got it by purchasing some steel rod from
www.onlinemetals. I think it was 6 or 8 mm rod. I can't remember! The pin and retaining slot was more of a nuisance as I had the mast erected by crane. Without it, we could have lifted it straight up and dropped it into the slotted center of the step plate. With the pin, we had to lean the mast aft, slide the base aft, slot it, and then raise it.
If I was erecting the mast by hand, I suppose the pin and slot would at least keep the mast base from sliding forward off the step plate as I winched it up or pulled it up using lines.
The bse and step plates can be found here:
http://www.rigrite.com/Spars/Zspar/Z-Mast_steps_hinged.html
Note that you cannot actually BUY these as, according to rigrite, they have been on backorder for 5+ years...
Thanks,
Andrew