Cynikal 

I'm going to start building racks this year and Santa is bringing me a rigid 400 series bender (I've clearly been a good boy). I'm trying to decide on what size bender to get. My primary question is, can I bend smaller diameter tubing on a bender? Example, If I get the 3/8's bender can I bend 5/16's and 1/4 with it as well?

I plan on doing several types of racks from rando style handlebar bag racks to porteur racks so I'm looking for some flexibility.

Thanks

Andrew R Stewart 

With the thin wall tubing we all like to use one really needs some tube side support to keep the tube from crimping or flaring out at the bend. This pretty much means a mandrel or form per tube OD and bend radius.So if I understand the question- I would not be bending a 1/4" tube with a 3/8" form. Andy

unterhausen

I bend 5/16" on a 5" diameter bend radius die for 1/2" (I think). And it doesn't flatten it. So it depends on what the radius of the bend is.

I would suggest that you get 5/16" because it's by far the most useful size. That's what I make my rando racks out of anyway. I built one out of 1/4" and decided it looked too wimpy. And I know Tubus makes stuff out of 3/8" (okay, 8mm), but I don't think that's really necessary.

I don't know if there is anything on ebay right now, but that's where I have gotten all of my tubing benders. Definitely lots of ridgid benders on ebay right now. Didn't scroll enough to see if there is a 405.

Definitely stick with the 400 series, and avoid the 39x series at all cost. I think those are made for soft copper, but there are usually broken ones on ebay.

Cynikal 

Thanks. This is really helpful. I also plan on making a 4-5" radius out of Alu, most likely with a V cut for the rando style racks. It's good to know that a wide radius is more forgiving. I'll go with the 405.