As others have said they do not fit 507. The slot in the replacement brush is too narrow, much smaller than the standard brushes that come with 507. You can force them (I did that once), but I didn't want to damage the brush and tape it shut (another reviewer) or have to buy a new 507 (it's an excellent electric brush). Came back for the 507. Those who say they are "perfect" for the 507 either got a different product than I did or they just put them in their place without much thought.
Wild Fuel Dental Probiotics: Fresh Breath & Healthy Bacteria Support - Vegan, Cruelty-Free Chewable Tablets for Oral Health - 45 Mint Flavored, Sugar-Free Travel Tin
14 Review
Convenient Listerine Ready! Tabs Whitening Chewable Tablets: Polar Mint Flavor to π¦· Combat Bad Breath, Whiten Teeth, and Eliminate Germs Anywhere, 24 ct, Sugar-Free, Gluten-Free
11 Review
BLIS Fresh Breath Kit: Potent BLIS K12 Oral Probiotic for Bad Breath & Halitosis Treatment - Clinically Proven Mouthwash, Tongue Scraper, Lozenges - 4 Week Supply
11 Review
π TheraBreath Fresh Breath Chewing Gum: ZINC with Citrus Mint Flavor - Pack of 6 (10 Count)
11 Review