Note: Helmets tend to run small. After measuring, manufacturer recommends ordering one size up.
Measure circumference of head and reference: Small (19"-20") Med.(21"-22") Large(23"-24") XL(25"-26")
COTTON CANVAS HELMET FOR DAVID CLARK HEADSETS
These defiantly run small. I have a small head. The wife calls me pin head. Normally a medium would be too loose. The medium is a little tight on me. I think it will be ok though. If you have a large head forget it.
Great fit, comfortable
This helmet is well designed and constructed with good canvas and nice leather trim. The leather keeper loop with snap for my google strap is an appreciated feature. The helmet fits my DC H-10-13 headset very well. I was able to order the correct size by first trying on a helmet at the Aircraft Spruce booth at Oshkosh.
With a 23 1/8 inch head, I found the Large Size to be uncomfortably tight. The Large size is 23-25 I'll send this back and get the XL(25-26) This helmet could do with some improvements in design. The old WW2 German helmets for example, had adjustments for head circumference. That sort of strap with Velcro would do wonders in providing a final adjustment. A tight helmet has a claustrophobic effect and not want you want for aerobatics.
Yes, it does.
Yes, this helmet will work with the Lightspeed headset.
Yes, the strap is velcro.
Yes, those headsets should work with this helmet.