Proper threaded insert for a square tube

[Wassercrats]

This is for something that I want to be fairly easy to build (no welding, tapping threads, expensive machinery, or buying large quantities). I want to attach a 1/4" bolt to the inside of a mild steel square tube that has a 3/8" ID and a 1/16" wall. The tube will support a small shelf and the bolt will stick out of the tube and be attached to a c channel. I bought some 1/4" x 1" drop-in anchors (basically threaded inserts), which have a 3/8" OD and are made for concrete. I could partially expand them, file a partial bevel on the unexpanded side, and hammer them in, or maybe expand them once their in by blocking the end of the tube so they don't get banged out. I think it will work, but is there a better choice of anchor for this?

 

[Compositepro]

http://www.mcmaster.com/#square-tube-inserts/=g0y0e5

This or similar.

 

[Wassercrats]

I don't think I did enough research into square tube inserts, but those particular ones wouldn't hold. There will be a lateral load. A small shelf will be attached to the top of two of these:

 

[hydtools]

Use the insert compositpro referenced and use all-thread through the length of the square tube and insert to pull the square tube tight to the channle with a nut.

Ted

 

[MintJulep]

Cross Threaded Dowel.

 

[Wassercrats]

Yeah, the dowel was a back-up plan. I tried the drop-in anchor first because there's no need to drill and it's self-centering. And drop-in anchors are cheaper than compositpro's inserts, and I'm not sure those inserts could accept a bolt through the rear.

I finally tried the drop-in anchor. I slightly expanded the end of the tube by hammering in a screwdriver, then I hammered in a slightly expanded drop-in anchor with a 4 lb sledge hammer. It's very strong and the threads didn't deform. I think I'll go with this.

I think I'll use the end caps I saw on that page though. I'll just sink the anchor deeper.