Bought a single edge razor and the blades I ordered don't fit it. Are SE blades not all the same?

Bit embarrassed posting this. I've been on a DE for about eight months and wanted to try a single edge, so I bought a secondhand SE razor off a mate at work and ordered a pack of "single edge razor blades" online at the same time.

They don't fit. Not even close. The blades are long with a folded metal strip on the back and the razor seems to want something narrower that slides in from the side. I assumed single edge was like DE where any blade goes in any razor.

Is there a way to tell what my razor takes? There's no name on it that I can find, just a number stamped on the underside of the head.

Welcome to the one thing nobody warns you about with SE. There isn't a single SE blade, there are several families and they don't swap.

From your description you've bought the spined type, the ones with the folded strip on the back. A razor that wants a blade sliding in from the side sounds like an injector style. Completely different blade, different shape, different loading. Post a photo of the head from the side and someone will know.

The number on the underside is your friend, search that plus "razor" and you'll probably find the model. Older razors often only have a patent number or a date code stamped there.

And keep the spined blades. They're handy for all sorts of things around the house and you might end up with a razor that takes them anyway. Ask me how many razors I own.

Robde has it. DE is close to universal, one blade shape fits nearly every DE razor ever made, and that has spoiled all of us. SE is the opposite: a handful of separate blade systems, each with its own razors, and a blade that doesn't fit its razor properly is a blade you should not be shaving with.

The order I'd go in is: identify the razor, identify which blade system it was made for, then buy a small pack of that blade only. If it turns out to be a fairly rare system, check that blades are still easy to buy before you get attached to it, because that's the real catch with some of the older SE razors.

For what it's worth, the shave itself needs almost nothing new from you. Same angle, same zero pressure, same with the grain first pass. The thing you will notice is that you can't flip the head, so you rinse more often. I wrote up how SE and DE razors compare in types of razors explained.

Found it from the number on the head. Injector, as Rob guessed. Blades are still made, not as many brands as DE but enough. Ordered a pack.

Update after a week and a half. Tom wasn't wrong about rinsing, I kept reaching to flip it for the first few shaves. But the shave is lovely, really quiet and steady, and on my chin, which always chatters with a DE, it just goes straight through.

Not ditching the DE, it's still the one that goes in the travel bag because the blades are everywhere. But I get the fuss now. And yes slantcurious, the spined blades are now scraping paint off a window frame.