The BSA Thunderbolt was one of the most popular of all of the A65/A50 models.  They were produced from 1966 to 1972.  

You can own a Thunderbolt t-shirt with the 1967 side cover design on the back.  The winged BSA logo is black printed on the front left chest.

 
The shirts are 6.1 oz. (heavy) 100% preshrunk cotton.  Far heavier than other 4.3 oz. shirts being sold.  6.0 to 6.4 oz. are the heaviest t-shirts available. 

Sizes available:
     Medium (M)
     Large (L) SOLD OUT 
     Extra Large (XL) SOLD OUT
     2 Extra Large (XXL) SOLD OUT 

Postage via first class mail. $4.00 SHIPPING (except international).  My cost to ship via USPS is now $5.00
Thanks for looking.  RIDE HARD!