Turn buckles might add in cost too, but they are re-usable if you want to take the wires down every year.

Tension bolts are cheap and come in several sizes. They have hooks at each end. My high tunnel is 48' long, and I strung chain above each row, tightened with a tension bolt. I didn't use it, though, because I was skeptical about the amount of weight it would hold. The chain was only rated at 80 pounds I think, and I was worried the row of tomatoes would weigh more than that.

what size wire are you using 7/16, 3/8 ?
what is " roller hook offs " ?
if it what I am thinking of we are both doing the same thing. if so I would use turn buckles, on at each end.
how big of a green house and how many rows of wire ?

Ah, turnbuckles. The better idea. I am way new at this obviously. Thank you.

Oops I didn't see the last two posts before I posted. Roller hooks, as in the strings on rolls that you hang on wires and can lower your tomatoes as they grow. My high tunnel is 16x24 and I am doing 5 rows of wire. Size of wire - I'd have to look it up again. I took the size Johnny's told me and my local feed store had it in stock for 9Maple) sugaring operations.

What's the difference between a tension bolt and a turnbuckle?

Sorry, they are the same thing. Turnbuckle is the more correct name.

is this a wire you use to trellis tomatoes instead of using twine attached to a purlin?

Rollerhook gizmos hang off of wire stretched across the high tunnel. You can see pics here, I tried to put a link on, we'll see if it works. that way you can harvest off the bottom of the plant, remove leaves, lower plant, slide it down the wire, and keep producing from the top.

Here is a link that might be useful: Tomato Rollerhook link

you could probably use a fence stretcher. generally called a daisy wheel.

ok your using the same thing I use in my greenhouse, if your running the wire the length of 24' X 5 rows. at every other truss add a rope from the top of the truss to the wire to help support the wire with the extra weight of the tomatoes. USE ROPE so you can adjust for the grow of the tomatoes if it becomes to heavy!!!

I am doing the same thing but over the span of 100' but I have "snow load cross pipe " on ever other truss. so I will run my wire on top of the cross pipes to make up for the extra weight of the tomatoes...

if this doesn't make sense I will post pics!!

Rope won't last very long inside a high tunnel unless it is UV protected. An alternate to rope is wire but if you want to do a better job support the roller hooks from perlins with a "S"-hook, one for each roller hook. "S" hooks come in any length you want from 6" to 36", are super sturdy and since they are directly attached to the perlin when you won't have many of of your roller hooks fly off a wire when you "twang" the wire...and it will happen.

I have not used the roller hooks but use the tomahooks. When I built my first high tunnel (20x96) I didn't think the frame would support the tomato weight and being impressed with high tensile fencing I burried telephone poles, braced and twitched, at each end of the high tunnel and strung 9 guage, 1800 lb, tensile strength wire through the high tunnel using a single open chain link and metal strap attached to arches to just hold the wire up. It works but I would never do that again. When I take one tomahook off the wire 5 others spring off as well

For my followup High tunnel (30x96) I have 8 perlins that the "S" hooks are always hanging from. I slide them along the perlin to position them when starting plants on stringline. Center perlins have longer "S" hooks, two tomato rows per perlin; side perlins have shorter ones. You still want your roller hooks at least 7-8 ft. high IMO to allow plants room to grow while keeping ripening fruit between knee and shoulder height. Your roller hooks will be easier to lower plants than my tomahooks but the price for 800 roller hooks puts them out of my price range. I got all of my tomahooks at auction for practically peanuts b/c nobody knew what they were.

So if you still want to tension the wire go to a Tractor Supply store or order the "In-line strainers" online from a high tensile fence supply outlet. Some strainers are meant to be tensioned with a special tool, others are tightened with a 1/2" rachet wrench. They are usually $2-$3 each and will last as long as your galvanized structure. Oh, the "S" hooks are available from greenhouse supply centers (ref. Nolts Supply, Leola, PA) and they cost ~$12- $37.50 (36") for bundles of 100.

bomser are you talking about Wire Extension Hangers for hanging baskets? they will work also.

lets not get the wrong idea, this wire doesn't need to be a tight as a piano wire. just get some turn buckles at home depot.

Boston, that's what they look like and they don't corrode either like the cheaper turnbuckles. If the wires aren't tight the tomato weight will cause wires to sag. If you price out the galvanized turnbuckles and in-line strainers you'll find that strainers are a better choice. However I have no inkling of the type of wire you are using. If the wire isn't SS or coated it may rust through in a few years.

bmoser I think there is some confusion, the turn-buckles is for either end of the wire to make it tight.

the Wire Extension Hangers or rope, is for supporting the wire from sagging from the weight of the tomatoes..

I picture exactly what you're saying but my point is that there is a better approach than suspending wire at all. My second point was that if Mt.topgarden insists on using wire method there is still a cheaper, longer lasting and easier to work with solution than turnbuckles.

bmoser have you started planting tomatoes yet in your big green house ? if so can you post a pic?

I will be planting this week I will do the same..

also how many tomato plants do you fit in your big house???