Bulb, Fuel gauge and Warning panel - copy
You'll find two kinds of bulbs aboard your Yak 52. These, with a slightly larger diameter metal ring around the contact end, are for the fuel gauge and also fit the warning lights in the binnacle display (above the instrument panels front and rear. )
The bulb for the gear and flap indicators have two ridges along their length and fit into slots in those lamp housings. The bulbs pictured here are NOT for the gear and flap indicators.