FITS MOST BULB HORNS...THIS IS THE LOW-COST BULB YOU'VE BEEN LOOKING FOR. Just screw it on and start honkin'! We offer bulbs in just two sizes: Large and Mini. Large is the "standard size" bulb and fits most bulb horns. Mini is designed for little "bicycle-size" horns. This Large Bulb fits Circular, Large, Small and Straight horns (does not fit Double Bell or Mini horns). Spare brass reed available separately if needed. IMPORTANT: Reed screws into horn, not the bulb. So if your reed screws into bulb, then our bulb will not work. (Yes, the reed slides inside bulb tube. But reed is physically attached to horn.) FITS THESE HORNS: Bulb fits virtually all vintage car, taxi, antique, old-brass and clown horns. Also fits Dobani product code: BULL, BULS, BULH, BULD, and BULO. HOW TO CHOOSE BULB SIZE: 1. Measure Bulb Tube. If outside diameter is 11/16" (17.5 mm), then get Large Bulb. If outside diameter is 5/8" (15.9 mm), then get Mini Bulb unless horn designed for large standard-size bulb. 2. Measure Brass Fitting. If horn fitting OD is 5/8" (15.9 mm), then get Large Bulb (same as Large Bulb tube ID). If horn fitting OD is ~9/16" (14.3 mm), then get Mini Bulb (same as Mini Bulb tube ID). 3. Measure Bulb. If bulb circumference is 11-1/2" (29.2 cm), or length from base to neck is 5-1/4" (13.3 cm), then get Large Bulb. If bulb circumference is 8-3/16" (20.8 cm), or length from base to neck is 3-1/4" (8.2 cm), then get Mini Bulb. WHY CHOOSE THIS BULB: If you want a brand new pre-tested budget-priced, antique-style, replacement bulb that fits most Circular, Large, Small and Straight bulb horns, then this bulb is for you. TECHNICAL SPECS: Bulb Diameter: 3-3/4" (9.5 cm), Bulb Circumference: 11-1/2" (29.2 cm), Bulb Length to end of brass collar: 5-1/4" (13.3 cm), Brass Tube Length: 1-1/2" (3.81 cm) more or less, Brass Tube ID (screw fitting): 5/8" (15.9 mm) at 28 tpi (threads per inch), Brass Tube OD: 11/16" (17.5 mm).