Garmin Part 010-10646-01 : Need authentic Garmin dash disks?  The windshield mounts adhere to this just like it does on your windshield.  This is 2.5 inches in diameter.

Fits many Aera, Nuvi, Dezl, and StreetPilot models including:

AERA: 500, 510, 550, 560

DEZL: 560LMT, 560LT

NUVI: 30, 40, 40LM, 50, 50LM, 200, 200W, 205, 205W, 250, 250W, 255, 255W, 260, 260W, 265T, 265WT, 275T, 370, 360, 350, 310, 300, 465T, 500, 550, 680, 670, 660, 650, 610, 600, 785T, 775T, 770, 765T, 760, 755T, 750, 885T, 880, 860, 855, 850, 1100, 1100LM, 1200, 1250, 1260T, 1300, 1300LM, 1350, 1350T, 1350LMT, 1370T, 1390T, 1390LMT,1450, 1450LM, 1450T, 1450LMT, 1490T, 1490LMT, 1690, 1695, 2200, 2250, 2250LT, 2300, 1300LM, 2350M 2350LMT, 2350LT, 2360LMT, 2360LT,  2370LT, 2450, 2450LM, 2450LMT, 2460LMT, 2460LT, 2555LT, 2555LMT, 2595LMT, 3450, 3450LM, 3490LMT, 3550LM, 3590LMT, 3750, 3760T, 3760LMT, 3760T, 3790T, 3790LMT, 5000

QUEST: 1 and 2

STREETPILOT: C310, C320, C330, C340, i2, i3, i5

Fits the following Zumo car cradles:  550, 500, 450, 400