Type 1 or type 11

[daniel2013]

Can someone please tell me what is the difference between a type 1 or a type 11 Thompson Center barrel?

[DEACONLLB]

Not real sure but any way type one did not have the split locking lug but someone could change that at some point in time time. Type two had the split locking lug and the barrel mounting lug had a small step in it. If this is not compleatly true Ladobe will put us streight
Deaconllb

[jbj-displays]

Only 6 different Type 1 barrels were made. 22LR,22 Mag,22 Jet, 22 Hornet, 38 Special, and 357 Mag. All being octagon barrels with the barrel markings being all in one line so Type 1 barrels are also known as one line barrels.
The type 2 barrels look like the Type 1 (both have the flat lug and short rear sights) difference being the markings are now not all in a line in the Type 2 versions. The number of chambers really took off at this time too. On ebay right now is a 17/222 Type 2 barrel for sale so you can see what they look like.
Justin

[Ladobe]

To expand on what justin posted...
 
There are several variations of Type I barrels in 8 3/4" and 10", some very rare (as are the very first frames that were flatsides); but basically the significant identifier is the addy: T/C Arms Rochester N.H. followed by the caliber; very first where in 22RF, 22WMR, 22 Jet, 22 Hornet and 38 SPL only before 357MAG was also added; all 1967 only.

There was an intermediate between Type I and Type II with a one line addy that is the caliber followed by T/C Arms Rochester N.H.; also 1967 only.
 
Type II; now with a two line addy that still has a period after both the N and H (after the H only in the two line Type III barrels); 1967-1972   I don't remember offhand how early in 1968, but they dropped the 8 3/4" length.   By the end of the T2's they had the largest cartridge selection.   IE, in 1968 they added 256WM and 45 Colt; in 1969 30 Ccarbine and 222Rem and by 1970 they were up to 25 cartridges for them including the Hot Shots and still going.
 
L.