Which Blade Adapter to use

What blade adapter can you use? The old models use to have a key so you could slide the adapter on. The new one I bought is flush! Please help!

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crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
crwdns2934285:0crwdne2934285:0