Recently BCA?s E&T Committee has briefly discussed screw in anchors.  I decided that although this was a piece of work still in progress, I felt it was worthy of being offered out for comment and also seek contributions on other persons experiences.  I have not fully searched ukCaving forum but think I have reflected the significant recent comments.

Screw in anchors are a simple bolt with a screw like body and usually a hexagonal shaped head.  They just require one to drill a hole into the rock and then simply screw the anchor into the hole, the anchor being self tapping.  A hanger is also required to enable one to attach a rope or whatever to the anchor.  Screw in anchors are also know by the name of one of the early manufacturers, Multi Monti.  Another popular name is Thunderbolt.

Screw in anchors are manufactured by a range of companies, some more reputable than others.  Some anchors are offered with a CE marking to meet certain European Technical Approvals for use in buildings.  None so far have been found to offer meeting the European Standard for Personal Protective Equipment and in particular EN 795:2012 for PPE anchors or EN 959:2007 for mountaineering anchors. 

Data supplied by some manufactures indicates that it is possible that their screw in anchors could meet the mountaineering anchors standard.  There is also some reports by other caving organisations (see http://ssf.ffspeleo.fr/fr/cellule-de-veille-technique/vos-questions-les-reponses-de-la-cvt/161-cellule-de-veille-technique/vos-questionsles-reponses-de-la-cvt/475-multi-monti-spits-goujonsq and https://cexcartagena.files.wordpress.com/2009/06/article_tornillos.pdf ), but to emphasise, it is not clear that these bodies are recommending their use. 

However experience in the UK has indicated that other manufacturers do not seem to have achieved the quality required by these standards.  In addition to the report by BMC (see https://www.thebmc.co.uk/bolt-failures-on-north-wales-limestone ) where the shaft sheared a small distance from the head, BCA?s Equipment and Techniques Committee has now received reports of several other unspecified failures in use.

It is a matter of speculation but failure modes could include:

? Insufficient material strength
? Manufacturing defects
? Over torquing the head during placement creating a incipient failure
? Corrosion between hanger and anchor made of different materials

In addition reports have also been made that the bolt can unscrew though the mechanism is as yet unclear.  A suggestion has been made that an application of a resin / glue the hole before screwing in the anchor helps bond the anchor in place and stops the unscrewing.  It has also been suggested that one might be able to reuse the hole and anchor.  This may well increase the potential for unscrewing.

The anchor does have one major positive conservation feature in that it is usually possible to unscrew and remove the anchor.

E&T do not at the moment have plans to test this type of anchor.  Given the information to hand, it seems difficult to provide any recommendation for the use of a screw in anchor.

I've used these a lot. Not in caving but in the building industry.

A couple of points if I may. I have, on occasion, managed to shear the head off. This has been using 100mm Thunderbolts into 2" (I know, but that's how it is!) timber. Unlikely to be overtorqued or it would just sink into the timber. My personal, unsubstantiated, theory is that the socket wasn't square to the head and twisted it somehow.

Resin or gluing the bolt in would somewhat defeat the object of the hole being reuseable and, as the thread 'taps' into the hole anyway, re-using the hole is probably a bad idea as, unless you are very lucky, you would end up making the hole just a little bit larger each time.

Also, never, EVER, reuse a Thunderbolt for anything important. If you look at the end of the thread it flattens out and goes blunt. Any previous thread that you have cut into the rock/stone is just getting bigger and you'll end up with a hole a bit bigger than you expected.

I've been using 8mm Excalibur bolts as temporary placements for a while now, and have been happy with them - although not sold for human use, their figures seemed reasonable for the projected applications, and I feel quite confident in them. And they're British. I did find out the hard way about re-using them though, as one jammed two thirds of the way in, probably for the reason outlined above, and I too snapped the head off, which was an eye-opener. So I'm only using them once now, but it does give the option of replacing one with a permanent stainless 10mm throughbolt (or a larger resin bolt) in a perfect placement in any final rigging, as the rock hasn't been pre-stressed, just cut.

http://excaliburscrewbolts.com/

thanks both.  I was after more experiences and the points made are useful additions.

I even managed to screw them into massive calcite crystals (with care), there being no useful rock at the height required. These two performed fine for a Y-hang, though were never shock-loaded:



Others fared less well in the crystals when holding a rigid ladder to the wall, but they were getting severe axial loading every climb, so not that surprising really.

Used them for equipping sport climbing routes initially, (8mm hole, 10mm hanger), which then enables them easily taken out to be re-positioned if not quite in the right place, leaving only a small hole which can be filled with a little resin, when the rest are taken out and re-drilled for putting resin P bolts in.  Quite happily falling on them in a lead climbing situation.  No failures.

I think the hardness of the rock is a big factor. I've sheared the head on a couple at home trying to screw them into very hard red brick.
I gave some to a mate for equipping a route at Kilnsey in the Yorkshire Dales, and he too could not get them to screw in at all as the limestone at that point was bullet hard.

I think over torquing is probably the mechanism by which the shear failures occur.

As I tighten them, I repeatedly give then a little back turn - i.e. one full turn tightening, one quarter turn to loosen, etc.  I suspect it worth loosening them slightly on the hanger, then nipping them tight again.  This will release any over torsion prior to just nipping them tight.

If your thinking of sustainable bolting, as Simon has suggested on the other thread, then I think you cant to too far wrong with these (as a temporary solution with a view to replacement with a resin bolt).

Oceanrower said:

I've used these a lot. Not in caving but in the building industry.

... I have, on occasion, managed to shear the head off. This has been using 100mm Thunderbolts...

Click to expand...

Oceanrower, Do you really mean Thunderbolts? Thunderbolt is the name of a specific brand but the term Thunderbolt is sometimes used generically in the construction industry. It is important to make the distinction clear. It's a shame that the BMC did not make it clear in their article.

Maybe you can clear it up. The is a good photo in the article. Can you identify the bolt as a Thunderbolt (the brand Thunderbolt)?

https://www.thebmc.co.uk/bolt-failures-on-north-wales-limestone

It was the other feller that referred to the Thunderbolts, not me. I've only used Excalibur bolts specifically - Mel Milner mentioned on here that they're been very resistant to wet conditions in the Manifold caves she'd used them in (for non-stainless), and I must say I have been quite impressed by the lack of issues so far, using stainless hangers.

Sorry pwhole it was Oceanrower.

Googling APT Thunderbolt (with or without quotes) just adds to the confusion. It appears there are things called "APT Thunderbolts".

https://www.orbitalfasteners.co.uk/en/categories/apt-thunderbolt-screwbolt-fixing-hxb-concreto-anchor-screw

Are they using 'Thunderbolt' generically? It's hard to know.

fwiw .. mine were multi monti

It looks like Thunderbolts are a brand name owned by A.P. Technik, who seem to now be owned (at least here) by Unifix. The bolts themselves look kosher:

http://unifix.co.uk/about-unifix

http://unifix.assets.workwithone.co.uk/sites/default/files/Thunderbolt%20DoP.pdf

A.P. Technik were dissolved in 2011.
https://beta.companieshouse.gov.uk/company/03223759

A.P. Technik used to make Thunderbolts and had an ETA.
http://products.vjtechnology.com/upload/ProductDocument/Thunderbolt-Tech-Spec--new06-.pdf

Hexstone have an ETA on Thunderbolts dated 2015. Thunderbolts and Ankerbolts are identical, are on the same ETA and are made in the same factory in Taiwan or at least they are claimed to be made in a factory which has a Taiwan address. http://www.metain.nl/uploads/bestanden/ETA_optie_1_Tapanker_CE.pdf

But Hexstone market the two bolts as different branded products through different subsidiaries. That begs the question, why would they do that?
http://jcpfixings.co.uk/sub-cat/ankerbolt
http://www.unifix.co.uk/thunderbolt

Do Thunderbolts have APT on the head simply because the Taiwan factory never changed the tooling?

The ones I generally have used are marked as Thunderbolts, normally from Travis Perkins. The ones similar that Screwfix sell really are crap!

Thanks Oceanrower. Screwfix currently sell Rawl LX Masonry Bolts and DeWalt Blue Tip Screwbolts.

The small size Dewalt ones have no ETA but 10mm and over carry an ETA. However, having perused a few of these ETAs I'm slightly suspicious. Apparently ETAs only cover products from a specified manufacturing plant and some companies appear reluctant to be entirely open about where products are made. The DeWalt ETA states that the manufacturing plant is "Manufacturing plant 1" - Hmm??
http://anchors.dewalt.com/pdf_files/eta_approvals/eta_12-0607.pdf?1411723685

DeWalt seem to specialize in mid range goods not of particularly high quality.

I can find little information on the Rawl LX Masonry Bolts. The Rawl price list says they are a new product and that approvals are 'pending'.