Bulkhead lamp knockouts

I'm referring to this bulkhead fitting:
http://www.tlc-direct.co.uk/Products/GLFIN1412.html
I ordered 4 of these recently. Nice fitting. However the knockouts don't seem to be knockouts at all - they are slightly recessed areas in the case which even a stiff blow with something sharp or a small ball pein hammer won't shift.
I suppose having tried the brute force technique I ought to give ignorance a try.
Anyone had problems with knockouts?
PoP
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The fittings are weather sealed and the knockout points are only marked to keep you in the centre when you drill them out with a hole saw.
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PoP wrote:

I found the same with the Screwfix ones I ordered.
In the end I used a sheet metal punch - the type where you drill a 10mm hole and then assemble the punch and coller through the hole before tightening the punch into the coller. Worked fine (after I worked out I had assembled the coller the wrong way round and the side I was using was intended for the next punch down in the size range - thought it was bl**dy stiff to turn!)
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On Tue, 14 Oct 2003 01:35:37 +0100, John Rumm

I am much relieved that I am not going completely bananas!

Good idea! What size punch are these holes anyway? I'll get my micrometer on the job later today.....
PoP
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3/4" or 20mm. If you think you'll do a lot of this sort of thing, get a Q-Max punch which produces a perfect hole, rather than a hole saw, and costs less than a complete single size hole saw. The disadvantage is you need access to both sides of the job.
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London SW 12

These are ideal if you're doing this type of job all time.
http://www.mustangtoolsandfixings.co.uk/ishop/978/shopscr5334.html
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PoP wrote:

I wanted about 20mm for connecting to plastic conduit. The punch I used was like the following set from CPC:
http://tinyurl.com/qwdj
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On Tue, 14 Oct 2003 18:43:18 +0100, John Rumm

I was looking for a set of cutters earlier today. Thanks for the link!
PoP
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I've had 2 of these lamps, only in black from local factors, and found the same problem. The plastic/polycarbonate seemed to be quite brittle so I didnt get rough with the hammer / punch / swrewdriver, so took a 20mm hole cutter to it which worked a treat.
Tim..
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