Thank you Nathan:

As always, you enlighten, whilst leaving my old head spinning. Chemistry was never my best subject.

Stainless steel passivates - it forms a coating of Chromium oxide (which ever number it is) which is hard and inert. Aluminium does the same thing, except that Al2O3 is dissolved by relatively weak OH-, in normal conditions this simply reforms on the surface, but in the presence of a different metal the reaction continues.

(I would be wary of SS in contact with Al in salt water conditions, or where regularly wet.)

Yes, aluminium alloys are generally too weak for bolts for the reasons you gave.

Nathan: Yes, that is what we were told, more or less. If memory serves, it goes back to a time long ago, before we replaced all of our windows with thermopanes and needed replacement screws to hold the aluminum frames of storm windows.

The man at our local hardware store (Oh, for the days of real hardware stores!) told us not to use anything but aluminum or SS, or the screws and/or aluminum frames would corrode.

He didn't explain WHY though, or I've forgotten, but your explaination would make sense, especially in a GH that uses water that has been treated for hardness.

But why is SS exempt? Or is it simply LESS prone to the reaction?

I think I understand why BC supplies only SS fasteners with their GH's instead of aluminum though: it's simply too soft for such use. Thinking back; that was why we needed new screws. We had removed the storm windows to paint the window frames and the aluminum screws furnished with them had stripped out in the process.

Whenever you have dissimilar metals you form a shorted battery when salty water bridges the gap between them. This will cause the metals to corrode.

heebiejeebie:

We were cautioned against it due to reaction of aluminum to base metals. If that was just an old wive's tale and untrue, then we have been taking unnecessary precautions.

However, SS is still a better idea for damp or wet locations and at least it has never left with the need to saw off fasteners when we wanted to remove them.

I don't know that zink is a problem in itself, but plated parts can lose their coating, so the real issue may be more what is under the zinc.

I am sure a metals expert will come along soon, to clarify and/or correct what I had been led to believe.

BIRDWIDOW:

You said:
"I'd be reluctant to use any zinc plated base metal including T bolts in direct contact with aluminum"

Why is that?

buyorse11888, you don't actually bolt into the greenhouse. The nuts or bolts slide into the frame channels. I did this while building my 6 x 8 HFGH and they have worked great. I use them for hanging items and those on the side for tying up plants by using eye-bolts into my captive nuts.

DH doesn't think the framework of the HFGH is strong enough to bolt anything to it.

If you want to cut 50 bolt heads, it would be much quicker to put a nut in a metal vice, screw the bolt in a reasonable distance and cut with an angle grinder with the thinest cut off disk you can find. I've got a 2mm thick disk for my angle grinder and it cuts through bolts like a knife through cheese.

Lets see, I can buy a bolt, nut and washer for about 30cAU, those commercial ones are about $2AU. A new cheap angle grinder and cut off wheel costs about $40, a new metal working vice costs about $60. You could pay the whole thing off with about 60 bolts! (and get an angle grinder and metal vice for your pains)

I never have bought from the internet I go to my local Fastenal store. I go their several times a year any time I need something that the big box stores don't usually carry I buy at Fastenal.

Gardener:

The channels to mount bolts on the polybars (studs) of the Cross Country are on the face and easy to access, with slightly wider "holes" interspaced along them, so I was thinking in terms of very little material being drilled out: just enough to allow the insertion of the head of a hex bolt.

From your caution about structural weakening; I suppose the HFGH studs are made differently.

I looked on the Fastenal site, but couldn't find the size bolt I need in smaller packages. Perhaps I didn't look in the right place.

Funny the subject came up when it did though, as we went to our local Menard's shortly after I posted that bit about the SS nuts and bolts and there, we found a package of SS 1/4-20 nuts at a right price: $5.99 for a pkg. of 144. (odd sort of number?)

But no all threaded SS 1/4-20 X 1/2" bolts, so I ordered a pkg. of 100 of them from Small Parts. They should be enough to attach all the electrical boxes, vinyl straps to hold the conduit, water lines, brackets for vinyl covered shelving, etc.

And, I won't need to waste any more time or get even more frustrated from running all over hinder and yon looking for them.

You can buy any size bolt that you want in SAE or Metric Zinc plated or stainless steel at FASTENAL.
Yes you can drill holes in the channel but it will weaken the wall stud by doing this. On the HFGH you can also remove the bolt from part #47 pull the wall stud out a little way and slide a bolt up the channel in the wall stud.

As I stated in my post above you use 1/4" bolts in the length that you need for whatever you are going to attach.
Some bolt have the head a little too thick grind a little off the head then grind it down to the shaft on two sides so it looks like a T then round the corners of two opposite corners so you can turn it and it will lock into the channel. Be sure to have a bucket of water to dip the bolt in to cool it.

buyorsell, show him the picture of the T-bolt in the link I posted above. Then find a bolt whose shaft will fit in your HFGH slot. Ask your DH to use his grinder to grind off the sides of a standard bolt to make it look like the one in the picture. He may have to flatten the head a little bit, too.

If you need more pictures, post back, and I can take some pics showing you how it fits in the slot and what to grind off, etc.

SB

My DH did not add any captive bolts at time of construction and does have a bench grinder.

Now, what pictures can I show him?

My HFGH is sitting practically empty and I'm getting nowhere. I am not handy and he won't read the computer........

The bench grinder idea is a good one, but if you need 50 bolts, it could take a while!

You are correct but since I'm retired I have more time than money. I also don't think you can buy three inch T bolts.

"Does tightening them keep them in place?"

Yes

The bench grinder idea is a good one, but if you need 50 bolts, it could take a while!

Why does it have to be a T type bolt?
why can't it be a regular bolt?
I still don't see what keeps them from sliding down the channel.
Does tightening them keep them in place?

well, DUH!!! (slaps forehead). A bench grinder! Never thought of that one.

Dave
Milwaukee

You can also make your own T bolts that is what I did.
I put 1 1/2" thick expanded polystyrene foam insulation on the wall and made T bolts from 1/4x3" bolts and used fender washers to secure the foam board to the wall.
You can buy the bolts for less than what you would pay for shipping on the bolts from the GH supply places.
If you don't own a bench grinder then you will need to use the high price option and buy them.

My GH uses 1/4-20 7/8" T-bolts. These can be added into the slot, secured with 1/8 turn and tightening, or removed as needed. Has anyone tried T-bolts with the HFGH? Will they fit in the channel? These are easy to come by and would allow the addition of shelves, etc even if you forgot to add the captive bolts at the time of construction. I'm sure one could find them cheaper than at this site below, but the picture is good.

Here is a link that might be useful: T-bolts

Captive Bolts are usualy Held in place using a Nut on the bolt.

if you are doing the reverse (using Captive Nuts, I Like this method, because they do not protrude when not in use), then you tighten a bolt into them far enough to wedge the nut into the channel.