3/8" Flex Cable Clamps

I've been using clamps like this for 3/8" Flex and 1/2" knockouts: <(Amazon.com product link shortened)>. They work fine, you just tighten the two bolts and the flex cable is gripped and strain-reliefed.
Home Depot had these that were a little cheaper and use only one bolt: <(Amazon.com product link shortened)>.
I must be doing something wrong here. The latter clamps, with the single bolt, do not grip the 3/8" flex cable even with the bolt tightened all the way down. What is the purpose of the clamp on these since the clamp is too big to grip the flex cable? I returned most of them to the store and bought the kind I'd been using. But I must be doing something really stupid for the single bolt type to not work.
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wrote:

Maybe not the right size? I think you have to look at the listing tho. Some may be listed for whips and others only when the cable is supported within a foot of the box. In that case, the clamp is not really holding that much.
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On 2/19/2015 2:00 AM, snipped-for-privacy@aol.com wrote:

I think the 2 screw model is for romex and the one screw unit is for greenfield or BX, although the 2 screw model could probably be used for BX or Greenfield too.
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wrote:

From 2 screw model: Sigma Electric C-510 BX/MC/FLEX 3/8-Inch Combination Connector
From 1 screw connector: Halex 90420 3/8-Inch Flex Squeeze Connector
Both should work fine if the flex is not distorted in the cutting process and is inserted and tightened properly. The second connector may have been switched with a 1/2 flex connector which may fail to tighten. I have used both geometries with success.
--
Mr.E

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wrote:

The "squeeze" type are only listed for installations where the cable is supported within 12" of the box. It's only function is to make an electrical connection, not a mechanical one. We used to fight them all the time under computer room floors.
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On 2/19/2015 10:54 AM, snipped-for-privacy@aol.com wrote:

So what is the purpose of tightening the screw and squeezing the clamp shut? It does nothing on 3/8" flex.
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wrote:

If it is not tight enough for an electrical connection, you have the wrong connector.
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On 2/19/2015 5:11 PM, snipped-for-privacy@aol.com wrote:

What does that mean? The clamp is essentially a strain relief to hold the aluminum sheath of the flex, mechanically. With the single screw clamp you tighten it all the way down but the diameter of the clamp is too large to grab the sheath of the 3/8" cable. I suppose that it also grounds it if the steel boxes are grounded through the outlet and switch tabs.
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wrote:

That sounds like a FMC clamp, not an MC cable clamp.
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On Thu, 19 Feb 2015 23:31:12 -0500, snipped-for-privacy@aol.com wrote:

Flexible Metal Conduit trade size is ID, OD is bigger so a 3/8 FMC will be about .61" MC cable is not the same thing. It actually ends up being .47" in 14-2 with ground. It is .49" in 12-2/wg
The NEC handbook says "FMC fittings are not considered to be a means of cable support."
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On Thu, 19 Feb 2015 23:59:39 -0500, snipped-for-privacy@aol.com wrote:

Try this one
http://www.homedepot.com/p/Halex-3-8-in-Flexible-Metal-Conduit-FMC-Snap-In-Connectors-5-Pack-26571/100202842
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wrote:

The bushing on the inside end says this is for a spiral armor cable, not NM
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