I think I know what you mean.
Are you talking about the bulges on the bonnet (hood)?
[url="http://cgi.ebay.co.uk/triumph-tr7-bonnet-spitfire-sports-car-mg-midget-tr6-/140414911179?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item20b16182cb"]Early type (Single bulge)[/url]
[url="http://cgi.ebay.co.uk/Triumph-TR7-Bonnet-/130400727152?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item1e5c7d3070"]Late type (Double bulge)[/url]
If that's the case, the single bulge bonnets were fitted to the early cars (Speke built, to 1979 or so?), the double bulge ones were fitted to the later cars (Canley/Solihull built, 1979 onwards). There's no real difference otherwise and they are interchangeable - unless you are fitting a V8, in which case you'll need the later type to clear the engine.
I hope that's what you meant! [:)]
Garry
1976 2.0 (soon to be 3.5!)FHC
http://reds-tr7.blogspot.com/