What kind of rotor arm is this?

I was about to change the plugs, distributor cap and rotor arm, with what I thought was the correct one like this;


 

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but when I took the cap off I found this


 

What kind of rotor arm do I need?  Is this a rev limiting one or something?

bottom one is a rev limiter type but has had its rev limiting mechanism removed.
not sure you can still get the limiting type anymore.

ah thanks, I thought it might be something like that.  So I can just use the other type no problem? 

can still get limiter type:
http://www.vwspares.co.uk/g1electrical.php

you can use non-limiter type no problem so long as its correct fitment for your dizzy, just no rev limiter obviously.

You are a helpful chap!  Thanks.  The car is running so much better already with new plugs and cap.

I'll swap over the arm too.  I don't plan to go anywhere near 6900 rpm!  Maybe order a rev limiting one for next time anyway.
 

Ahh, I wondered this myself when I was changing it over. Ended up ordering the rev limiting type off eBay £13 as I wasn't sure what it did.  That makes sense though.

Here's mine with the rev limter still intack.