I own several contemporary to motorized bicycle spark plugs.
That one, which can be seen on photo - is 1969 (1960-something, well, dont remember exactly) "A11У" spark plug.
What can I tell about it...
It is quite "hot" spark plug, made for low-forced engines, such as D4.
Soviet mark "A11" means similar like Bosch W9AC. Dont remember exactly, what means "У" in mark, it is either material "uranite" or something about wrench size.
16 mm wrench, 14х1,25 мм
Made by factory in Ufa city, factory, seems, is still alive: ÓÀÏÎ - Óôèìñêîå Àãðåãàòíîå Ïðîèçâîäñòâåííîå îáúåäèíåíèå - ñâå÷è çàæèãàíèÿ, íàñîñû, ýëåêòðîäâèãàòåëè
Works quite fine, as I can understand.
Here can be seen one of old Soviet spark plugs a little closer:
That one, which can be seen on photo - is 1969 (1960-something, well, dont remember exactly) "A11У" spark plug.
What can I tell about it...
It is quite "hot" spark plug, made for low-forced engines, such as D4.
Soviet mark "A11" means similar like Bosch W9AC. Dont remember exactly, what means "У" in mark, it is either material "uranite" or something about wrench size.
16 mm wrench, 14х1,25 мм
Made by factory in Ufa city, factory, seems, is still alive: ÓÀÏÎ - Óôèìñêîå Àãðåãàòíîå Ïðîèçâîäñòâåííîå îáúåäèíåíèå - ñâå÷è çàæèãàíèÿ, íàñîñû, ýëåêòðîäâèãàòåëè
Works quite fine, as I can understand.
Here can be seen one of old Soviet spark plugs a little closer: