There are two sizes.  I bet the stems you bought originally had the 87-91
grey knobs.  Those are impossible to find, so you will probably have to try
to make yours fit or think of something else..

>From: Michael Diehr <md03@XOCHI.COM>
>Reply-To: Michael Diehr <md03@XOCHI.COM>
>To: vanagon@GERRY.VANAGON.COM
>Subject: Stove Knobs -- 2 sizes?
>Date: Sun, 15 Jan 2006 22:02:05 -0800
>
>I just replaced the 2 burners on my 85 westy stove with ones bought
>off ebay.   All works fine, except the stems on the replacement unit
>are larger diameter, so the knobs don't seem to fit.   Does anyone
>know if there are 2 sizes of knobs?  Or do you just have to push
>really hard and/or ream out the knob to make it fit?