Replacing MM Base Rings

I just placed an order for a replacement base ring for my JB. I received a message wondering if I’m sending the cage back, since they can’t promise the new one will fit without it. Being in the UK, I’d rather avoid additional postage fees and waiting time.

What has been your experience? Has anyone purchased just the base rings while keeping their existing cages? Did you run into any issues?

The key issue seems to be locating where to drill the hole for the lock. You can place your current ring flat and measure up to the center of that opening, then send them those numbers. Even if you're off by 1/16th", it likely won't matter. Also, consider using 'inch' measurements. We Americans are often too confident to bother with metric.

Why not pick up a vernier caliper for just a few quid and measure it yourself? That said, keeping the cage means there's always some risk involved. I actually ordered two rings along with mine as insurance.

I'd send it back. Since their products are fully custom-made, the new ring is unlikely to fit your cage perfectly unless they have your specific cage on hand during production.

A couple of years ago, I purchased a MM QK and opted for two base rings because I wasn't entirely sure about my measurements. It didn't take long to realize the smaller one (1 3/4") fit better, and soon after I wished I had kept that size. Last year around this time, I bought a gently used MM WM from another member here on the forum. It came with a 1 5/8" ring and was constructed to match the gap of my existing QK. For these devices at least, it turns out the rings are completely compatible.

I own two MM devices. Both feature a security hole designed for a plastic lock. The screw holes on these units are fully interchangeable between cage and ring, but the security holes are not. If you don't use that specific security hole setup, I'd try ordering just the base ring.

Mine uses a padlock. Do you think that will work fine?

That's basically my point too. The extra hole needed for the plastic lock requires the base ring and cage to line up perfectly. When I swap rings and cages using just the screw, it works without issue. That’s really the only difference between a MM device configured with a screw versus one with a padlock in those threads. You can definitely use a padlock if you prefer. With just that single hole and matching gap sizes, I don't see why the cage would need to be sent back. Maybe email William at MM directly? Ask him specifically why he recommends it return, citing what we've all discussed here. We aren't as knowledgeable about their specific quirks as he is. Perhaps he's seen other issues that haven't affected us yet.