diff --git a/src/main/scala/net/kemitix/s3thorp/S3MetaData.scala b/src/main/scala/net/kemitix/s3thorp/S3MetaData.scala
index 01ec002..6139acc 100644
--- a/src/main/scala/net/kemitix/s3thorp/S3MetaData.scala
+++ b/src/main/scala/net/kemitix/s3thorp/S3MetaData.scala
@@ -1,8 +1,8 @@
 package net.kemitix.s3thorp
 
-import net.kemitix.s3thorp.Sync.{Hash, LastModified, LocalFile, RemotePath}
+import net.kemitix.s3thorp.Sync.{MD5Hash, LastModified, LocalFile, RemoteKey}
 
 case class S3MetaData(localFile: LocalFile,
-                      remotePath: RemotePath,
-                      remoteHash: Hash,
+                      remotePath: RemoteKey,
+                      remoteHash: MD5Hash,
                       remoteLastModified: LastModified)
\ No newline at end of file
diff --git a/src/main/scala/net/kemitix/s3thorp/Sync.scala b/src/main/scala/net/kemitix/s3thorp/Sync.scala
index 9e7a138..cb61cbb 100644
--- a/src/main/scala/net/kemitix/s3thorp/Sync.scala
+++ b/src/main/scala/net/kemitix/s3thorp/Sync.scala
@@ -5,6 +5,7 @@ import java.time.Instant
 
 import cats.effect._
 import net.kemitix.s3thorp.Main.putStrLn
+import net.kemitix.s3thorp.Sync.{Bucket, LocalFile, RemoteKey}
 import net.kemitix.s3thorp.awssdk.S3Client
 
 class Sync(s3Client: S3Client)
@@ -13,8 +14,8 @@ class Sync(s3Client: S3Client)
     with UploadSelectionFilter
     with S3Uploader {
 
-  override def objectHead(bucket: String, key: String)=
-    s3Client.objectHead(bucket, key)
+  override def objectHead(bucket: Bucket, remoteKey: RemoteKey)=
+    s3Client.objectHead(bucket, remoteKey)
 
   def run(c: Config): IO[Unit] = for {
     _ <- putStrLn(s"Bucket: ${c.bucket}, Prefix: ${c.prefix}, Source: ${c.source}")
@@ -32,8 +33,8 @@ object Sync {
 
   type Bucket = String // the S3 bucket name
   type LocalFile = File // the file or directory
-  type RemotePath = String // path within an S3 bucket
-  type Hash = String // an MD5 hash
+  type RemoteKey = String // path within an S3 bucket
+  type MD5Hash = String // an MD5 hash
   type LastModified = Instant // or scala equivalent
 
 }
diff --git a/src/main/scala/net/kemitix/s3thorp/UploadSelectionFilter.scala b/src/main/scala/net/kemitix/s3thorp/UploadSelectionFilter.scala
index a2e8609..4318d04 100644
--- a/src/main/scala/net/kemitix/s3thorp/UploadSelectionFilter.scala
+++ b/src/main/scala/net/kemitix/s3thorp/UploadSelectionFilter.scala
@@ -2,13 +2,13 @@ package net.kemitix.s3thorp
 
 import fs2.Stream
 import cats.effect.IO
-import net.kemitix.s3thorp.Sync.{Hash, LocalFile}
+import net.kemitix.s3thorp.Sync.{MD5Hash, LocalFile}
 import java.security.{MessageDigest, DigestInputStream}
 import java.io.{File, FileInputStream}
 
 trait UploadSelectionFilter {
 
-  private def md5File(localFile: LocalFile): Hash =  {
+  private def md5File(localFile: LocalFile): MD5Hash =  {
     val buffer = new Array[Byte](8192)
     val md5 = MessageDigest.getInstance("MD5")
 
diff --git a/src/main/scala/net/kemitix/s3thorp/awssdk/ReactiveS3Client.scala b/src/main/scala/net/kemitix/s3thorp/awssdk/ReactiveS3Client.scala
index a4876c8..7406da1 100644
--- a/src/main/scala/net/kemitix/s3thorp/awssdk/ReactiveS3Client.scala
+++ b/src/main/scala/net/kemitix/s3thorp/awssdk/ReactiveS3Client.scala
@@ -4,16 +4,17 @@ import cats.effect.IO
 import com.github.j5ik2o.reactive.aws.s3.S3AsyncClient
 import com.github.j5ik2o.reactive.aws.s3.cats.S3CatsIOClient
 import software.amazon.awssdk.services.s3.model.{HeadObjectRequest, NoSuchKeyException}
+import net.kemitix.s3thorp.Sync.{Bucket, LocalFile, RemoteKey}
 import software.amazon.awssdk.services.s3.{S3AsyncClient => JavaS3AsyncClient}
 
 private class ReactiveS3Client extends S3Client {
 
   private val s3Client = S3CatsIOClient(S3AsyncClient(JavaS3AsyncClient.create))
 
-  override def objectHead(bucket: String, key: String) = {
+  override def objectHead(bucket: Bucket, remoteKey: RemoteKey) = {
     val request = HeadObjectRequest.builder()
       .bucket(bucket)
-      .key(key)
+      .key(remoteKey)
       .build()
     try {
       for {
diff --git a/src/main/scala/net/kemitix/s3thorp/awssdk/S3Client.scala b/src/main/scala/net/kemitix/s3thorp/awssdk/S3Client.scala
index e7dbec0..4cf8517 100644
--- a/src/main/scala/net/kemitix/s3thorp/awssdk/S3Client.scala
+++ b/src/main/scala/net/kemitix/s3thorp/awssdk/S3Client.scala
@@ -1,11 +1,11 @@
 package net.kemitix.s3thorp.awssdk
 
 import cats.effect.IO
-import net.kemitix.s3thorp.Sync.{Hash, LastModified}
+import net.kemitix.s3thorp.Sync.{Bucket, MD5Hash, LastModified, LocalFile, RemoteKey}
 
 trait S3Client {
 
-  def objectHead(bucket: String, key: String): IO[Option[(Hash, LastModified)]]
+  def objectHead(bucket: Bucket, remoteKey: RemoteKey): IO[Option[(MD5Hash, LastModified)]]
 
 }