you can use 25mm(c2c) bus bar for 4s1p. it is available from aliexpress "CHLBATT Factory Store"
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In case of 4s3p, 55mm(c2c) bus bar can connect 3p by drill 6mm hole at center with regular drill, screw two end to scrap board to easy the drilling. 35mm(c2c) bus bar to connect 3p to 4s. both can be purchased from same store
55mm(c2c)
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35mm(c2c)
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took about two weeks to get it by AliExpress Standard Shipping.
here is my 1s4p and 8s6p, there is 30mm(c2c) bus bar bought from
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Plastic cover is cutting from pencil case bought from Amazon
Amazon.com : MotBach 6 Pieces Transparent Frosted Pencil Case, Plastic Stationery Storage Case, Clear Pencil Box with Hinged Lid and Snap Closure for Pencils, Pens, Concise Style Box for School and Office : Office Products
www.amazon.com