The Truth about Parallel Clamps and Why They’re Hard to Review

Video - April 3, 2023

I recently purchased twelve* different brands of parallel clamps in hopes of reviewing them all. Unfortunately, I failed in my mission to come up with a fair and balanced set of parameters for testing. I did, however, uncover some interesting truths about parallel clamps that I think you need to know. So if you’re in the market for parallel clamps, you should be aware of these things as a parallel clamp setup is a substantial investment. So here’s The Truth about Parallel Clamps and Why They’re Hard to Review.

1. The heads on a parallel clamp should not necessarily be square!

I noticed that many clamp reviewers will test the squareness of the clamp head to the bar and rely on it as a metric for overall build quality. They assume that an out-of-square head is a problem. I’ve even seen some companies using the squareness of their clamping heads as a selling point. The reality is that having a toed-in head is actually desirable. The parallel clamp was originally designed by Bessey in 1980 and the heads were deliberately toed-in. And they’re still manufactured that way today. Simply put, the toe-in helps the clamp achieve a parallel state while under pressure .

Of the twelve brands we have on hand, half of them feature square heads. You might be wondering, should those clamps be avoided? I don’t necessarily think so, but ultimately it’s up to you. You may have specific reasons for preferring your clamps be square in their resting state. Personally, I prefer the toe-in as it makes the most sense to me. So while I’m not saying a square head is necessarily a negative, I am saying that a toed-in head is definitely NOT a flaw and should instead be viewed as an intentional feature.

2. All parallel clamp bars deflect under pressure.

No matter which brand you buy, the bar on a parallel clamp will deflect under pressure, raising up at the center and sloping down near the clamp heads. This ties directly into Truth #1. If the clamp heads are toed-in, the deflected bar will change the effective angle of the clamp head so that while under pressure, the two clamp heads are parallel. If the heads are not toed-in, they will start parallel and end up out of parallel under pressure should enough pressure be applied. I’ve seen numerous reviews of parallel clamps that test the amount of deflection of the bar and unless they also include some way to regulate the amount of force being applied on the clamp, the resulting measurements will be fairly meaningless.

3. Maybe parallel clamps aren’t the best solution for clamping panels?

I say this last point with some apprehension because I’ve been clamping panels with parallel clamps for ages. Based on Truths #1 and #2, it’s clear that the very nature of parallel clamps is that they will cause a panel to bow when under pressure. But in most cases, this isn’t a serious problem since we don’t need to apply full pressure to close the joints and wood is often more resilient than we give it credit for. But if absolute flatness is critical for your work, you might consider a different style of clamp.

Hopefully this arms you with information that will not only help you when shopping for parallel clamps, but also help you evaluate current reviews more critically. I’m not sure I’ll ever be able to pull off a full shootout style review of parallel clamps, but I can give you one piece of advice. Regardless of the brand, pretty much EVERY parallel clamp will get the job done. Some may be better built with higher-quality materials. Others may have toed-in heads and creature comfort features that make the clamp easier or more fun to use. But in pretty much every case, the clamp will hold your work together until the glue dries, and that’s really the point, isn’t it? At least for now, my buying advice is to get the clamp that you can get on sale and then stop reading and watching reviews.

*Easy links to the 12 brands you see in the video in no particular order:

Bessey –
Jorgensen –
Bora –
Rockler Parallel Clamps
Irwin –
Dewalt –
Harbor Freight (Bremen)
Peachtree –
Woodpecker (Semble)
Yost –
Bessey I-Beam Clamps –
Rockler Mini Deluxe Panel Clamps


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