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1 whole unit can be split into 1,000 equal parts. Each part is one thousandth. 
Or we can show the same thing this way:
One (1) whole unit  
Split into ten equal parts (tenths)  
Each tenth split into ten equal parts (hundredths)  
Each hundredth split into ten equal parts  
Each part is one thousandth 
When we write numbers with thousandths using decimals we use a decimal point and places to the right of this decimal point. The thousandth place is three places to the right of the decimal point.
389/1000 = .389  .  3  8  9 
We read this number as three hundred eightynine thousandths 
Blocks  Fraction  Decimal  Notes 
1/1000 
.001 one thousandth 

2/1000 
.002 two thousandths 

37/1000 
.037 thirtyseven thousandths 
Note: three hundredths = thirty thousandths 

104/1000 
.104 one hundred four thousandths 
Note: one tenth = one hundred thousandths ( .1 = .100) 

545/1000 
.545 five hundred fortyfive thousandths 

1 1/1000 
1.001 one and one thousandth 

1 263/1000 
1.263 one and two hundred sixtythree thousandths 
The worksheets below will help practice working with decimals and place values to the right of the decimal point.