Bulb, Flap/Gear Indicator
You'll find two kinds of bulbs aboard your Yak 52. These, for the gear and flap indicators located in the cheek panels to the left of the instrument panels, are retained by threaded bezels, and push into housings that have two matching ridges along their length.
(The bulbs with a slightly larger diameter metal ring around the contact end, are for the fuel gauge and also the warning lights in the binnacle display above the instrument panels front and rear.
The bulbs pictured on this page are NOT for the fuel gauge