On a Cag there M5 x 0.8 x 20-25mm long, you can tap it to M6 x 1.0 with the right drill and tap. H/F tools has metric tap & dies set cheap onsale. For $20 onsale can get an SAE & Metric set together.
Easy as pie!!!!!! Nice job getting it done...I retapped all my reedblock holes to M6 1.0 in my reeded engines for the same exact reason of the problem you had..My bottom left hole just stripped out for no reason...My guess would be that there was an inexperienced chinese kid working on hundreds maybe thousands of engine cases with the same problem/defect and never caught it.....I just used my friends HF tap and die set. M6x1.0